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Measurement, STD2 2026 HSC 15 MC

A scientist is estimating the population of a bee colony.

The scientist captures \(p\) bees but only marks \(k\%\) of them and releases them all back into the colony. The next day, the scientist captures \(q\) bees and finds that \(r\) bees were marked.

Assuming all bees have an equal chance of being captured, which expression gives the best estimate of the total bee population?

  1. \(\dfrac{kpq}{100r}\)
  2. \(\dfrac{100r}{kpq}\)
  3. \(\dfrac{q(p-k)}{100r}\)
  4. \(\dfrac{r}{q}-\dfrac{kp}{100}\)
Show Answers Only

\(A\)

Show Worked Solution

\(\text{Let $N$ = bee population}\)

\(\text{Capture} = \dfrac{\frac{k}{100}\times p}{N} = \dfrac{kp}{100N}\)

\(\text{Recapture} = \dfrac{r}{q}\)

\(\text{Since capture/recapture ratios are equal:}\)

\(\dfrac{kp}{100N}\) \(=\dfrac{r}{q}\)  
\(\dfrac{100N}{kp}\) \(=\dfrac{q}{r}\)  
\(N\) \(=\dfrac{kpq}{100r}\)  

 
\(\Rightarrow A\)

Filed Under: Ratios Tagged With: Band 6, smc-6931-30-Capture/Recapture

Financial Maths, STD2 2026 HSC 38

Maya plans to go on an overseas trip in 5 years' time. Maya expects that the trip will cost \(\$14\ 000\). To save for the trip, Maya began by contributing \(\$750\) every 6 months into an annuity. After making a number of payments, Maya realised that the annuity would not reach \(\$14\ 000\) in 5 years. Maya decides to double the contribution until the trip.

The interest rate was 2% per annum compounding half yearly.

Future values of an annuity of $1
Rate Period 0.01 0.02 0.03 0.04
2 2.0100 2.0200 2.0300 2.0400
4 4.0604 4.1216 4.1836 4.2465
6 6.1520 6.3081 6.4684 6.6330
8 8.2857 8.5830 8.8923 9.2142
10 10.4622 10.9497 11.4639 12.0061
12 12.6825 13.4121 14.1920 15.0258

 
What is the maximum number of \(\$750\) contributions Maya could make before she will need to double her payments to reach \(\$14\ 000\)? (4 marks)

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\(2\ \text{contributions}\)

Show Worked Solution

\(\text{Find annuity total of \$750 payments only:}\)

\(r=\dfrac{0.02}{2}=0.01,\ \  n=5\times2=10\)

\(\text{Table factor = 10.4622}\)

\(\text{Value of annuity} = 750 \times 10.4622=\$7846.65\)

\(\text{Extra money needed (at end of annuity)}\ = 14\ 000-7846.65=\$6153.35\)
 

\(\text{Estimated table factor where \$750 annuity has a total \$6153.35}\)

\(750 \times\ \text{Factor}\ = 6153.35\ \ \Rightarrow \ \ \text{Factor} = \dfrac{6153.35}{750} = 8.20 \ldots\)

\(\text{Using the table:}\)

\(\text{8 periods at  $r=0.01$  is the lowest that will create an annuity > \$6153.35}\)

\(\text{Since there are 10 contributions, only 2 can be \$750 only.}\)

Filed Under: Annuities (Y12) Tagged With: Band 6, smc-6912-10-FV of $1 Annuity Table

Statistics, STD2 2026 HSC 36

A group of students participated in a coding challenge. The times taken to complete the challenge are normally distributed with a mean of 60 minutes and a standard deviation of 10 minutes.

  1. In a random sample of 2000 students, how many students would be expected to take between 40 and 70 minutes to complete the challenge?   (2 marks)

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  2. Only the fastest three students of the 2000 students qualified for a national challenge.
  3. What was the maximum time needed to qualify?   (2 marks)

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a.    \(\text{Approximately }1630\text{ students}\)

b.    \(30\ \text{minutes}\)

Show Worked Solution

a.    \(z\text{-score (40)} = \dfrac{40-\mu}{\sigma} = \dfrac{40-60}{10} = -2\)

\(z\text{-score (70)} = \dfrac{40-\mu}{\sigma} = \dfrac{70-60}{10} = 1\)

\(\text{68% of times have a $z$-score between $-1$ and $1$.}\)

\(\text{13.5% of times have a $z$-score between 1 and 2.}\)

\(\Rightarrow \text{% of times with a $z$-score between $-1$ and $2$} = 68+13.5 = 81.5\%\)
 

\(\text{Expected number}=2000\times 0.815 = 1630\ \text{students}\)
 

b.    \(\dfrac{3}{2000}\times100\%=0.15\%\)

\(\text{Since 99.7% of times have a $z$-score between $-3$ and $3$,}\)

\(\text{0.15% of times are below a $z$-score of $-3$.}\)

\(\text{Find time with $z$-score = $-3$:}\)

\(-3\) \(=\dfrac{x-60}{10}\)  
\(x-60\) \(=-3 \times 10\)  
\(x\) \(=30\)  

 
\(\therefore\ \text{Maximum qualifying time}= 30\ \text{minutes}\)

Filed Under: The Normal Distribution (Y12) Tagged With: Band 4, Band 6, smc-6919-10-Single z-score, smc-6919-20-z-score Intervals

Measurement, STD2 2026 HSC 33

A rectangular tub has length 50 cm, width 20 cm and unknown height \((h)\).

Ten identical cylinders are arranged inside the tub in two rows of five.

Each cylinder has diameter 10 cm and height \(h\) cm.

Exactly 3 litres of water is poured into the tub to fill all the spaces around the cylinders.
 

What is the height of the tub, correct to the nearest whole number?    (4 marks)

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\(14\ \text{cm}\)

Show Worked Solution

\(\text{Water volume}=3\times1000=3000\ \text{cm}^3\)

\(\text{Tub width = 20 cm = 2 × cylinder diameter}\)

\(\text{Cylinder radius}\ = \dfrac{20}{4}=5\ \text{cm}\)

\(\text{Tub volume (method 1)}\ = 50 \times 20 \times h = 1000h\)
 

\(\text{Using cylinder volume}\ = \pi \times r^{2} \times h:\)

\(\text{Tub volume (method 2)}\ = (10 \times \pi \times 5^{2} \times h) +3000 = 250\pi h +3000\)

\(\text{Equating volumes:}\)

\(1000h\) \(=250\pi h +3000\)
\(h(1000-250\pi)\) \(=3000\)
\(h\) \(=\dfrac{3000}{1000-250\pi}\)
  \(=13.979\ldots \text{cm}\)

 
\(\therefore\ \text{Height of tub = 14 cm (nearest whole)}\)

Filed Under: Volume, Mass and Capacity Tagged With: Band 6, smc-6304-50-Volume (Circular Measure)

Measurement, STD1 2026 HSC 31

A ship sails 8 km from \(A\) to \(B\) on a bearing of 070°. It then sails from \(B\) to \(C\).

Point \(D\) lies on the line \(CE\) and is 5 km due east of \(B\), and \(E\) is 8.7 km due south of \(C\) and directly east of \(A\).
 

What is the true bearing of \(A\) from \(C\), correct to the nearest degree?   (4 marks)

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\(235^{\circ}\)

Show Worked Solution

\(\text{In}\ \Delta ABF:\)

\(\angle BAF=90-70=20^{\circ}\)

\(\cos 20^{\circ}\) \(=\dfrac{AF}{8}\)
\(AF\) \(=8\cos 20^{\circ}=7.517…\ \text{km}\)

 
\(FE=BD=5\ \text{km}\)

\(AE=7.517…+5=12.517…\ \text{km}\)
 

\(\text{In}\ \Delta ACE:\)

\(\tan \angle ACE\) \(=\dfrac{12.517…}{8.7}\)
\(\angle ACE\) \(=55.19…^{\circ}\)

 

\(\text{Bearing of}\ A\ \text{from}\ C\) \(=180+55.19…\)
  \(=235^{\circ}\ \text{(nearest degree)}\)

Filed Under: Right-angled Triangles (Y12) Tagged With: Band 6, smc-6834-60-Bearings

Networks, STD1 2026 HSC 27

The network shows the lengths of the paths between some exhibits at a zoo.
 

Nikolai is visiting the penguins and wants to visit the lions. The shortest path Nikolai can take is Penguins—Giraffes—Snakes—Lions.

  1. The paths around the zoo are not all flat. The network shows the same paths at the zoo with the gradients of each.
     
  2. Nikolai uses a wheelchair to get around the zoo. The wheelchair cannot access paths with a gradient greater than 0.083.
  3. Explain why the shortest path is not necessarily the best path for Nikolai to take to get to the Lions.   (1 mark)

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  4. What is the best path for Nikolai to take from the Penguins to the Lions?   (1 mark)

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  5. The speeds, in metres per second, that Nikolai can travel in the wheelchair are shown on some of the paths.
     
  6. Feeding time at the Lions is 12:15 pm. Nikolai plans to travel from the Otters to the Lions, passing the Koalas without stopping.
  7. What is the latest time Nikolai can leave the Otters to arrive for feeding time at the Lions?   (3 marks)

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a.    \(\text{The shortest path uses Penguins}-\text{Giraffes (gradient 0.11) and}\)

\(\text{Giraffes}-\text{Snakes (gradient 0.09).}\)

\(\text{Both gradients are greater than 0.083, so Nikolai’s wheelchair}\)

\(\text{cannot access these paths.}\)

b.    \(\text{Penguins}-\text{Bears}-\text{Otters}-\text{Koalas}-\text{Lions}\)

c.    \(\text{11:55 am}\)

Show Worked Solution

a.    \(\text{The shortest path uses Penguins}-\text{Giraffes (gradient 0.11) and}\)

\(\text{Giraffes}-\text{Snakes (gradient 0.09).}\)

\(\text{Both gradients are greater than 0.083, so Nikolai’s wheelchair}\)

\(\text{cannot access these paths.}\)
 

b.    \(\text{Penguins}-\text{Bears}-\text{Otters}-\text{Koalas}-\text{Lions}\)

\(\text{(all gradients on this path are less than 0.083)}\)
 

c.    \(\text{Using}\ \ \text{Time}=\dfrac{\text{distance}}{\text{speed}}:\)

\(\text{Otters to Koalas}\) \(=\dfrac{400}{0.8}=500\ \text{seconds}\)
\(\text{Koalas to Lions}\) \(=\dfrac{700}{1}=700\ \text{seconds}\)

 

\(\text{Total time}\) \(=500+700\)
  \(=1200\ \text{seconds}\)
  \(=20\ \text{minutes}\)

 
\(\text{Latest time to leave}=\text{12:15 pm}-20\ \text{minutes}=\text{11:55 am}\)

Filed Under: Rates, Shortest Path Tagged With: Band 4, Band 6, smc-6527-10-Network Diagrams, smc-6859-20-General Rate Problems

Measurement, STD1 2026 HSC 29

The floor plan of a house has been drawn using a scale of \(1:100\).
 

  1. What is the width of the bedroom in metres?   (1 mark)

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  2. The western wall of the living room is to be painted.
  3. The wall is 2.7 m high and the windows are 900 mm high.
  4. One litre of paint covers 12 square metres.
  5. How many litres of paint are required for two coats of paint? Give your answer to 2 decimal places.   (3 marks)

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a.    \(3.6\ \text{m}\)

b.    \(2.34\ \text{L}\)

Show Worked Solution

a.   \(\text{Using 1000 mm = 1 metre:}\)

\(\text{Width}=3600\ \text{mm}= \dfrac{3600}{1000}\ \text{m} = 3.6\ \text{m}\)
 

b.    \(\text{Western wall length}=5600\ \text{mm}=5.6\ \text{m}\)

\(\text{Window on western wall: 1200 mm wide (1.2 m), 900 mm high (0.9 m)}\)

\(\text{Area to paint}\) \(=\text{Wall area}-\text{Window area}\)
  \(=5.6\times 2.7-1.2\times 0.9\)
  \(=15.12-1.08\)
  \(=14.04\ \text{m}^2\)

 
\(\text{Two coats}=2\times 14.04=28.08\ \text{m}^2\)

\(\text{Paint required}=\dfrac{28.08}{12}=2.34\ \text{L}\)

Filed Under: Rates, Ratios Tagged With: Band 4, Band 6, smc-6858-20-Floor Plans, smc-6859-20-General Rate Problems

Financial Maths, STD1 2026 HSC 30

An amount of $3500 is invested for 3 years at an interest rate of 5.75% per annum, compounded annually.

Find the simple interest rate per annum that will give the same future value. Give your answer as a percentage, correct to 2 decimal places.    (4 marks)

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\(6.09\%\)

Show Worked Solution
\(FV\) \(=PV(1+r)^n\)
  \(=3500(1+0.0575)^3\)
  \(=\$4139.13\)

 
\(\text{Interest earned}=4139.13-3500=\$639.13\)

\(\text{Using}\ \ I=Prn:\)

\(639.13\) \(=3500\times r\times 3\)
\(r\) \(=\dfrac{639.13}{10\ 500}\)
  \(=0.06087…\)
  \(=6.09\%\ \text{(2 d.p.)}\)

Filed Under: Investment (Y12) Tagged With: Band 6, smc-6831-10-Simple Interest, smc-6831-20-FV Formula

Statistics, STD1 2026 HSC 22

The stem-and-leaf plot shows the age of 24 volunteers at a charity event.
 

\(\begin{array}{c|l}
\text{Stem} & \quad \quad \text{Leaf} \\
\hline \rule{0pt}{2.5ex}1 & \ 3\ \ \ \ 5 \\
2 & \ 0\ \ \ \ 2\ \ \ \ 5 \\
3 & \ 0\ \ \ \ 2\ \ \ \ 4\ \ \ \ 6 \\
4 & \ 1\ \ \ \ 3\ \ \ \ 3\ \ \ \ 7\ \ \ \ 8\ \ \ \ 9 \\
5 & \ 0\ \ \ \ 2\ \ \ \ 2\ \ \ \ \textbf{X} \\
6 & \ 1\ \ \ \ 4\ \ \ \ 6\ \  \\
7 & \ 0\ \ \ \ 2\ \  \\
\end{array} \qquad \qquad \boxed{\begin{array}{l} \text{KEY:} \\ 3\,|\,2=32 \end{array}}\)
 

  1. Describe the shape of the distribution.   (1 mark)

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  2. It is known that the upper quartile of the dataset is 55.
  3. Find the value of \(\textbf{X}\).   (2 marks)

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a.    \(\text{Approximately symmetric}\)

b.    \(\textbf{X}=8\)

Show Worked Solution

a.    \(\text{Approximately symmetric}\)
 

b.    \(\text{24 data values}\ \Rightarrow\ Q_3\ \text{is the average of the 18th and 19th values}\)

\(\text{18th value}=52, \ \ \text{19th value}=50+\textbf{X}\)

\(\dfrac{52+(50+\textbf{X})}{2}\) \(=55\)
\(102+\textbf{X}\) \(=110\)
\(\textbf{X}\) \(=8\)

Filed Under: Displaying Data - Other Charts Tagged With: Band 5, Band 6, smc-6531-10-Stem-and-Leaf

HMS, TIP EQ-Bank 111

Discuss how environmental conditions and group strengths and weaknesses influence the strategies and tactics used in ONE group sport.   (8 marks)

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Sport: Football (soccer)

Environmental Conditions

  • [P] Weather and ground conditions influence which tactics a football team can use well.
  • [E] Rain makes the ball skid and the ground heavy, so short passes along the ground become less reliable. Heat increases fatigue, so a high-tempo game is harder to sustain.
  • [Ev] For example, a team that usually builds play with short passes from defence may switch to longer passes into the attacking half on a waterlogged pitch. In hot conditions, the same team may slow the tempo and keep possession so that opponents do more of the running.
  • [L] This shows that coaches adjust tactics to suit the conditions, which reduces errors and helps manage fatigue.
     
  • [P] However, conditions can change during a match, which limits how much tactics can be planned in advance.
  • [E] A team that prepares a game plan for dry conditions may need to change tactics mid-match if heavy rain starts.
  • [Ev] For example, a passing team caught in a sudden downpour must quickly shift to more direct play, and players who have not practised this may struggle to adapt.
  • [L] This shows that changing conditions can reduce the value of pre-planned strategies, so teams also need to train tactical flexibility.

Group Strengths and Weaknesses

  • [P] Effective strategies are built around what the team does best.
  • [E] Matching tactics to the players’ abilities gives the team its best chance of gaining an advantage over the opposition.
  • [Ev] For example, a team with fast wingers may defend in a compact shape and then counter-attack quickly into the space left behind opponents.
  • [L] This shows that group strengths determine the main attacking strategy a team adopts.
     
  • [P] Strategies must also protect the team’s weaknesses from being exploited.
  • [E] Opponents will target any area where the team is vulnerable, so tactics are designed to limit that exposure.
  • [Ev] For example, a team with slow central defenders may defend closer to their own goal, reducing the space behind them that fast opposition attackers could run into.
  • [L] This shows that weaknesses influence defensive tactics as much as strengths shape attacking ones.
     
  • [P] However, environmental conditions can stop a team from using its strengths.
  • [E] A strategy built around the team’s best players may not work when the conditions take away the advantage those players give.
  • [Ev] For example, the counter-attacking team with fast wingers may struggle on a waterlogged pitch, where long passes stop short in the water and players cannot reach full speed.
  • [L] This shows that coaches must weigh both factors together and prepare alternative tactics, rather than relying on one game plan.
Show Worked Solution

Sport: Football (soccer)

Environmental Conditions

  • [P] Weather and ground conditions influence which tactics a football team can use well.
  • [E] Rain makes the ball skid and the ground heavy, so short passes along the ground become less reliable. Heat increases fatigue, so a high-tempo game is harder to sustain.
  • [Ev] For example, a team that usually builds play with short passes from defence may switch to longer passes into the attacking half on a waterlogged pitch. In hot conditions, the same team may slow the tempo and keep possession so that opponents do more of the running.
  • [L] This shows that coaches adjust tactics to suit the conditions, which reduces errors and helps manage fatigue.
     
  • [P] However, conditions can change during a match, which limits how much tactics can be planned in advance.
  • [E] A team that prepares a game plan for dry conditions may need to change tactics mid-match if heavy rain starts.
  • [Ev] For example, a passing team caught in a sudden downpour must quickly shift to more direct play, and players who have not practised this may struggle to adapt.
  • [L] This shows that changing conditions can reduce the value of pre-planned strategies, so teams also need to train tactical flexibility.

Group Strengths and Weaknesses

  • [P] Effective strategies are built around what the team does best.
  • [E] Matching tactics to the players’ abilities gives the team its best chance of gaining an advantage over the opposition.
  • [Ev] For example, a team with fast wingers may defend in a compact shape and then counter-attack quickly into the space left behind opponents.
  • [L] This shows that group strengths determine the main attacking strategy a team adopts.
     
  • [P] Strategies must also protect the team’s weaknesses from being exploited.
  • [E] Opponents will target any area where the team is vulnerable, so tactics are designed to limit that exposure.
  • [Ev] For example, a team with slow central defenders may defend closer to their own goal, reducing the space behind them that fast opposition attackers could run into.
  • [L] This shows that weaknesses influence defensive tactics as much as strengths shape attacking ones.
     
  • [P] However, environmental conditions can stop a team from using its strengths.
  • [E] A strategy built around the team’s best players may not work when the conditions take away the advantage those players give.
  • [Ev] For example, the counter-attacking team with fast wingers may struggle on a waterlogged pitch, where long passes stop short in the water and players cannot reach full speed.
  • [L] This shows that coaches must weigh both factors together and prepare alternative tactics, rather than relying on one game plan.

Filed Under: Types of training and training methods Tagged With: Band 4, Band 5, Band 6, smc-5465-05-Environmental, smc-5465-10-Group strengths/weaknesses

HMS, TIP NSE-Bank 29

Refer to the information below as well as your own knowledge to answer the question.

The information relates to the treatment of a sports injury.

A player is tackled in a football game and feels pain in their shoulder. During the assessment of the injury, the sports trainer identifies that the player has sustained a shoulder dislocation. The coach instructs the player to apply cold compression, immobilise their shoulder and completely rest for the next four weeks so that they can play in the grand final.

 
Evaluate the coach’s advice and propose a suitable rehabilitation program for the football player.   (12 marks)

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Evaluation Statement (coach’s advice)

  • The coach’s advice to immobilise the shoulder and completely rest for four weeks is inappropriate, as both strategies could negatively affect the player’s recovery and ability to perform successfully in the grand final.

Immobilising the Shoulder

  • Immobilising the shoulder for four weeks would dramatically decrease range of motion, increase joint stiffness and could result in muscle atrophy.
  • While immobilisation may initially protect the injured shoulder, prolonged immobilisation could negatively affect recovery.
  • As a result, the player may have reduced shoulder function when returning to play, increasing the risk of re-injury and restricting performance.

Complete Rest

  • Completely resting for four weeks would also negatively affect the player’s total body fitness, particularly the cardiorespiratory endurance required for football.
  • The player’s VO₂ max, haemoglobin levels and lactate threshold could decrease, resulting in increased fatigue.
  • This would reduce the player’s ability to meet the demands of the match and could cause skills such as tackling technique to deteriorate as the match progresses.

Final Evaluation

  • Overall, the coach’s advice is inappropriate because the negative effects on shoulder function and physical fitness outweigh the benefits of prolonged rest and immobilisation.

 
Proposed rehabilitation

  • Progressive mobilisation – gradually increasing range of motion for the injured shoulder.
  • Graduated exercise – includes stretching the injured shoulder allowing for increased muscle length and elasticity. Conditioning ensures that the injured shoulder has maintained its strength so that muscle atrophy doesn’t occur. Total body fitness that is sport specific should be maintained to avoid reversibility.
  • Training – ensuring that the athlete is at appropriate sport-specific fitness capacity to compete in the grand final. This can be achieved by playing in modified game situations during training sessions or playing in a reserve game as well as ensuring that the athlete’s timing, speed and coordination are all at pre-injury state.
  • Use of heat and cold – cold can assist in the reduction of inflammation as required.
Show Worked Solution

Evaluation Statement (coach’s advice)

  • The coach’s advice to immobilise the shoulder and completely rest for four weeks is inappropriate, as both strategies could negatively affect the player’s recovery and ability to perform successfully in the grand final.

Immobilising the Shoulder

  • Immobilising the shoulder for four weeks would dramatically decrease range of motion, increase joint stiffness and could result in muscle atrophy.
  • While immobilisation may initially protect the injured shoulder, prolonged immobilisation could negatively affect recovery.
  • As a result, the player may have reduced shoulder function when returning to play, increasing the risk of re-injury and restricting performance.

Complete Rest

  • Completely resting for four weeks would also negatively affect the player’s total body fitness, particularly the cardiorespiratory endurance required for football.
  • The player’s VO₂ max, haemoglobin levels and lactate threshold could decrease, resulting in increased fatigue.
  • This would reduce the player’s ability to meet the demands of the match and could cause skills such as tackling technique to deteriorate as the match progresses.

Final Evaluation

  • Overall, the coach’s advice is inappropriate because the negative effects on shoulder function and physical fitness outweigh the benefits of prolonged rest and immobilisation.

 
Proposed rehabilitation

  • Progressive mobilisation – gradually increasing range of motion for the injured shoulder.
  • Graduated exercise – includes stretching the injured shoulder allowing for increased muscle length and elasticity. Conditioning ensures that the injured shoulder has maintained its strength so that muscle atrophy doesn’t occur. Total body fitness that is sport specific should be maintained to avoid reversibility.
  • Training – ensuring that the athlete is at appropriate sport-specific fitness capacity to compete in the grand final. This can be achieved by playing in modified game situations during training sessions or playing in a reserve game as well as ensuring that the athlete’s timing, speed and coordination are all at pre-injury state.
  • Use of heat and cold – cold can assist in the reduction of inflammation as required.

Filed Under: Management/prevention of injuries Tagged With: Band 4, Band 5, Band 6, smc-5472-30-Management, smc-5472-40-Rehabilitation, smc-5472-60-Stimulus

HMS, HAG NSE-Bank 28

Refer to the information below as well as your own knowledge to answer the question.

City X is an urban area with a large number of young people, aged 10–24. The infographic provides information about City X.

To what extent could the application of Sustainable Development Goal 3: Good Health and Wellbeing and Sustainable Development Goal 4: Quality Education assist in improving the health status of young people in City X?   (12 marks)

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Judgment Statement

  • SDG 3 and SDG 4 can significantly improve the health, wellbeing and opportunities of young people in City X by increasing access to education, employment and health knowledge, although improvements depend on greater participation in tertiary education and positive health behaviours.

Educational and Employment Impact

  • The infographic shows that City X has high academic results in secondary school which are not reflected in participation in tertiary education.
  • SDG 4 supports young people to have equal access to all levels of education, which is particularly important given City X has a high migrant population, some of whom may speak languages other than English at home.
  • Increasing participation in tertiary education and relevant workplace training can improve employment opportunities and income.
  • Increased and stable incomes can support healthy eating and physical activity, increase the ability to access and afford healthcare services, and reduce stress.
  • Therefore, increased educational attainment can lead to positive health and welfare outcomes and support the fulfilment of SDG targets.

Health Literacy and Disease Prevention

  • SDG 3 and SDG 4 can also improve health outcomes by increasing health literacy and knowledge.
  • Greater education can improve understanding of the importance of immunisation and vaccination programs.
  • This can reduce the risks, health issues and mortality rates associated with communicable diseases.
  • Education can also increase a person’s ability to effectively use health information and increase the likelihood of engaging in positive health behaviours.

Physical Activity and Recreational Behaviour

  • The data reflects low participation in recreational activity, which can be addressed through SDG 3’s promotion of healthy lifestyles and prevention of premature mortality.
  • Greater participation in tertiary education can lead to greater employment opportunities and income, providing young people with the education and resources to choose a healthy diet and engage in physical activity through initiatives such as community sport.
  • This can reduce the risk of health issues and mortality associated with obesity.
  • The data also reflects a high proportion of unsafe recreational activity. SDG 3 supports safer recreational activities by preventing substance abuse and smoking, while SDG 4 can improve education and employment opportunities.
  • Together, these can reduce individual and family stress and reliance on harmful drugs and unsafe recreational activities.

Reaffirmation

  • Therefore, SDG 3 and SDG 4 can improve the health and wellbeing of young people in City X to a significant extent.
  • Increasing participation in tertiary education can improve employment, income, health literacy and access to healthcare while encouraging healthier behaviours and safer recreational activities.
  • The connection between SDG 3 and SDG 4 demonstrates that improved educational opportunities can contribute substantially to better health and wellbeing outcomes.
Show Worked Solution

Judgment Statement

  • SDG 3 and SDG 4 can significantly improve the health, wellbeing and opportunities of young people in City X by increasing access to education, employment and health knowledge, although improvements depend on greater participation in tertiary education and positive health behaviours.

Educational and Employment Impact

  • The infographic shows that City X has high academic results in secondary school which are not reflected in participation in tertiary education.
  • SDG 4 supports young people to have equal access to all levels of education, which is particularly important given City X has a high migrant population, some of whom may speak languages other than English at home.
  • Increasing participation in tertiary education and relevant workplace training can improve employment opportunities and income.
  • Increased and stable incomes can support healthy eating and physical activity, increase the ability to access and afford healthcare services, and reduce stress.
  • Therefore, increased educational attainment can lead to positive health and welfare outcomes and support the fulfilment of SDG targets.

Health Literacy and Disease Prevention

  • SDG 3 and SDG 4 can also improve health outcomes by increasing health literacy and knowledge.
  • Greater education can improve understanding of the importance of immunisation and vaccination programs.
  • This can reduce the risks, health issues and mortality rates associated with communicable diseases.
  • Education can also increase a person’s ability to effectively use health information and increase the likelihood of engaging in positive health behaviours.

Physical Activity and Recreational Behaviour

  • The data reflects low participation in recreational activity, which can be addressed through SDG 3’s promotion of healthy lifestyles and prevention of premature mortality.
  • Greater participation in tertiary education can lead to greater employment opportunities and income, providing young people with the education and resources to choose a healthy diet and engage in physical activity through initiatives such as community sport.
  • This can reduce the risk of health issues and mortality associated with obesity.
  • The data also reflects a high proportion of unsafe recreational activity. SDG 3 supports safer recreational activities by preventing substance abuse and smoking, while SDG 4 can improve education and employment opportunities.
  • Together, these can reduce individual and family stress and reliance on harmful drugs and unsafe recreational activities.

Reaffirmation

  • Therefore, SDG 3 and SDG 4 can improve the health and wellbeing of young people in City X to a significant extent.
  • Increasing participation in tertiary education can improve employment, income, health literacy and access to healthcare while encouraging healthier behaviours and safer recreational activities.
  • The connection between SDG 3 and SDG 4 demonstrates that improved educational opportunities can contribute substantially to better health and wellbeing outcomes.

Filed Under: Application of SDGs 3, 4, 10 & 11 Tagged With: Band 4, Band 5, Band 6, smc-5492-05-Applications and Lessons, smc-5492-40-Integrated evaluation

HMS, HAG NSE-Bank 26b

Explain how TWO approaches to health used in other OECD countries could be used in Australia to improve health outcomes. Provide examples to support your answer.   (8 marks)

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Show Answers Only

Other OECD approaches 

New Zealand Government: Recognition of the distinct health needs of Maori people is seen in:

  • partnership, or working together with iwi (tribes), hapu (sub-tribes/kinship groups), whanau (family groups) and Maori communities.
  • the involvement of Maori at all levels of decision-making, planning, development and delivery services.
  • the government working to ensure Maori have at least the same level of health as non-Maori, and safeguarding Maori cultural concepts, values and practices.

United Kingdom: Soft Drinks Industry Levy (“Sugar Tax”)

  • The UK applies a levy to UK-produced or imported soft drinks that contain added sugar. This is known as the Soft Drinks Industry Levy or colloquially as the “Sugar Tax”.
  • It was introduced to reduce childhood obesity.
  • The revenue from the levy has also been used to fund programs for childhood obesity.

How approaches could be used

  • Prioritising and funding Aboriginal and Torres Strait Islander community-controlled health services
  • Supporting health service providers to improve cultural safety
  • Ensuring better communication between healthcare services and patients
  • Improving coordination of healthcare services
  • Introducing economic approaches to addressing chronic health conditions
  • Making unhealthy choices less affordable
  • Applying tax from unhealthy products to fund programs that address health concerns.
Show Worked Solution

Other OECD approaches 

New Zealand Government: Recognition of the distinct health needs of Maori people is seen in:

  • partnership, or working together with iwi (tribes), hapu (sub-tribes/kinship groups), whanau (family groups) and Maori communities.
  • the involvement of Maori at all levels of decision-making, planning, development and delivery services.
  • the government working to ensure Maori have at least the same level of health as non-Maori, and safeguarding Maori cultural concepts, values and practices.

United Kingdom: Soft Drinks Industry Levy (“Sugar Tax”)

  • The UK applies a levy to UK-produced or imported soft drinks that contain added sugar. This is known as the Soft Drinks Industry Levy or colloquially as the “Sugar Tax”.
  • It was introduced to reduce childhood obesity.
  • The revenue from the levy has also been used to fund programs for childhood obesity.

How approaches could be used

  • Prioritising and funding Aboriginal and Torres Strait Islander community-controlled health services
  • Supporting health service providers to improve cultural safety
  • Ensuring better communication between healthcare services and patients
  • Improving coordination of healthcare services
  • Introducing economic approaches to addressing chronic health conditions
  • Making unhealthy choices less affordable
  • Applying tax from unhealthy products to fund programs that address health concerns.

Filed Under: Uncategorized Tagged With: Band 4, Band 5, Band 6, smc-5476-30-Lessons for Australia

HMS, TIP NSE-Bank 25

Analyse how the principles of progressive overload and training thresholds could be applied to a cyclist’s aerobic training program to improve performance. Provide examples to support your answer.   (8 marks)

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Overview Statement

Progressive overload and training thresholds each connect to a cyclist’s aerobic performance through physiological adaptations that improve the delivery and use of oxygen.

Component Relationship 1

Progressive overload can be effectively used to improve a cyclist’s aerobic performance by gradually increasing the frequency, duration and/or intensity of training.

Once the cyclist has adapted to their training program, this can be achieved by increasing the duration of sessions from one hour to 75 minutes.

This increased training stress on the cardiovascular and respiratory systems results in physiological adaptations, including increased haemoglobin and stroke volume levels.

These adaptations mean the cyclist can delay fatigue and maintain performance for longer, resulting in a faster time.

Component Relationship 2

Training thresholds connect to aerobic performance by ensuring that training occurs at an intensity above the aerobic threshold and below the anaerobic threshold, within the aerobic training zone.

To improve the performance of a cyclist, this would involve the athlete cycling continuously at 70–80% MHR within their training program.

Training at this intensity results in physiological adaptations including increased oxygen uptake and stroke volume.

These adaptations enable the cyclist to train and compete at a higher intensity for a longer duration because their heart is more efficient in delivering oxygen to the working muscles.

Implications and Synthesis

The relationships demonstrate that progressive overload and training thresholds work together to produce physiological adaptations that improve aerobic performance.

Overall, applying both principles enables the cyclist to delay fatigue, maintain a higher intensity for longer and achieve a faster performance time.

Show Worked Solution

Overview Statement

Progressive overload and training thresholds each connect to a cyclist’s aerobic performance through physiological adaptations that improve the delivery and use of oxygen.

Component Relationship 1

Progressive overload can be effectively used to improve a cyclist’s aerobic performance by gradually increasing the frequency, duration and/or intensity of training.

Once the cyclist has adapted to their training program, this can be achieved by increasing the duration of sessions from one hour to 75 minutes.

This increased training stress on the cardiovascular and respiratory systems results in physiological adaptations, including increased haemoglobin and stroke volume levels.

These adaptations mean the cyclist can delay fatigue and maintain performance for longer, resulting in a faster time.

Component Relationship 2

Training thresholds connect to aerobic performance by ensuring that training occurs at an intensity above the aerobic threshold and below the anaerobic threshold, within the aerobic training zone.

To improve the performance of a cyclist, this would involve the athlete cycling continuously at 70–80% MHR within their training program.

Training at this intensity results in physiological adaptations including increased oxygen uptake and stroke volume.

These adaptations enable the cyclist to train and compete at a higher intensity for a longer duration because their heart is more efficient in delivering oxygen to the working muscles.

Implications and Synthesis

The relationships demonstrate that progressive overload and training thresholds work together to produce physiological adaptations that improve aerobic performance.

Overall, applying both principles enables the cyclist to delay fatigue, maintain a higher intensity for longer and achieve a faster performance time.

Filed Under: Principles of training Tagged With: Band 4, Band 5, Band 6, smc-5460-10-Progressive overload, smc-5460-20-Thresholds

Financial Maths, STD2 2020 HSC 37 (Adapted)

Estelle deposits a single lump sum into an account that earns 3% per annum compound interest.

Present value interest factors for an annuity of $1 for various interest rates \((r)\) and numbers of periods \((N)\) are shown in the table.

  

From this account, Estelle plans to make the following withdrawals.

  • $2000 at the end of each year for the first 15 years (the first withdrawal is one year after the deposit).
  • $5000 at the end of each year for a further 10 years, that is, in years 16 to 25.

Find the smallest lump sum Estelle must deposit so that both sets of withdrawals can be made.   (3 marks)

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\(\text{Lump sum required}=\$51\,251\)

Show Worked Solution

\(\text{Annuity 1:}\ \ PV\ \text{of}\ \ \$2000\ \text{annuity for 15 years at}\ r=0.03\)

\(\Rightarrow PV\ \text{factor}=11.938\)

\(\therefore\ PV\ \text{Annuity 1}=11.938\times 2000=\$23\,876\)
  

\(\text{Annuity 2:}\ \ PV\ \text{of}\ \ \$5000\ \text{annuity for years 16−25 at}\ r=0.03\)

\(PV\ \text{Annuity 2}\) \(=PV(25\ \text{years})-PV(15\ \text{years})\)  
  \(=5000\times 17.413-5000\times 11.938\)  
  \(=5000\times(17.413-11.938)\)  
  \(=\$27\,375\)  

 
\(\therefore\ \text{Lump sum required}=23\,876+27\,375=\$51\,251\)

Filed Under: Annuities (Y12-X) Tagged With: adapted, Band 6, smc-7701-20-PV of $1 Annuity Table

Financial Maths, STD2 EO-Bank 34

Farah wants to buy a commercial espresso machine for her cafe at a cost of $4200. She has decided to pay off whatever she owes in a single amount 75 days after the purchase, and is weighing up two ways to fund it.

  • A credit card that compounds interest daily at 17% per annum, but does not charge interest during the first 25 days after a purchase.
  • A personal loan on which simple interest is charged at 8.9% per annum.

Advise Farah on the cheaper option, backing up your recommendation with the relevant calculations.   (4 marks)

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\(\text{Credit card interest}=\$98.93\)

\(\text{Personal loan interest}=\$76.81\)

\(\text{As }\$76.81\lt\$98.93,\text{ Farah should choose the personal loan.}\)

Show Worked Solution

\(\text{Days accruing interest}=75-25=50\)

\(\text{Credit card option (interest compounds daily):}\)

\(\text{Amount owing}\) \(=4200\left(1+\dfrac{0.17}{365}\right)^{50}\)
  \(=4298.931\ldots\)
  \(=\$4298.93\ \text{(nearest cent)}\)

 
\(\therefore\ \text{Interest}=4298.93-4200=\$98.93\)
  

\(\text{Personal loan option (simple interest applies):}\)

\(I=Prn\) \(=4200\times 0.089\times\dfrac{75}{365}\)
  \(=76.808\ldots\)
  \(=\$76.81\ \text{(nearest cent)}\)

  
\(\therefore\ \text{As }\$76.81\lt\$98.93,\text{ the personal loan}\)

\(\text{is cheaper, so Farah should choose it.}\)

Filed Under: Credit Cards (Y12-X) Tagged With: Band 5, Band 6, smc-7729-10-Interest on Purchases, smc-7729-50-Interest Free Periods, smc-7729-60-Other, syllabus-2027

Measurement, STD2 M1 2009 HSC 25b (Adapted)

The mass of a sample of hungry cat fleas is 0.675 kilograms. There are approximately `1.5 × 10^6` hungry cat fleas in the sample.

In standard form, what is the approximate mass in grams of one hungry cat flea?   (2 marks)

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`4.5 xx 10^-4\ text(grams)`

Show Worked Solution

`text(Convert 0.675 kilograms into grams:)`

`0.675\ text(kg) = 0.675 xx 1000 = 675\ text(g)`

`:.\ text(Mass of 1 flea)` `= text(mass of sample)/text(# fleas)`
  `= (675)/(1.5 xx 10^6)`
  `= 4.5 xx 10^-4\ text(grams)`

Filed Under: Identify and Convert Between Units (Y11-X) Tagged With: Band 6, smc-7730-20-Capacity/Volume/Mass, smc-7730-40-Scientific Notation

Financial Maths, STD2 EQ-Bank 32

Yasmin is planning to purchase a Newcastle Knights corporate box for $5000. She intends to repay the entire amount 90 days after making the purchase.

She is comparing two credit options.

  • Credit card: compound interest charged daily at 18% per annum, with a 30-day interest-free period from the date of purchase.
  • Personal loan: simple interest charged at 9.5% per annum.

Determine which option Yasmin should choose, showing calculations to support your answer.   (4 marks)

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\(\text{Credit card (daily compound interest):}\)

\(\text{Days accruing interest}\ =90-30=60\)

\(\text{Amount owing}\) \(= 5000\left(1+\dfrac{0.18}{365}\right)^{60}\)
  \(= 5150.118\ldots\)
  \(= \$5150.12\ \text{(nearest cent)}\)

  
\(\text{Interest} = 5150.12-5000 = \$150.12\)
  

\(\text{Personal loan (simple interest):}\)

\(I = Prn\) \(=5000 \times 0.095 \times \dfrac{90}{365}\)
  \(= 117.123\ldots\)
  \(= \$117.12\ \text{(nearest cent)}\)

 

\(\therefore\ \text{Since \$117.12 < \$150.12, Yasmin should choose the personal loan.}\)

Show Worked Solution

\(\text{Days accruing interest}\ =90-30=60\)

\(\text{Credit card (daily compound interest):}\)

\(\text{Amount owing}\) \(= 5000\left(1+\dfrac{0.18}{365}\right)^{60}\)
  \(= 5150.118\ldots\)
  \(= \$5150.12\ \text{(nearest cent)}\)

  
\(\text{Interest} = 5150.12-5000 = \$150.12\)
  

\(\text{Personal loan (simple interest):}\)

\(I = Prn\) \(=5000 \times 0.095 \times \dfrac{90}{365}\)
  \(= 117.123\ldots\)
  \(= \$117.12\ \text{(nearest cent)}\)

  

\(\therefore\ \text{Since \$117.12 < \$150.12, Yasmin should choose the personal loan.}\)

Filed Under: Credit Cards, Credit Cards Tagged With: Band 5, Band 6, smc-6847-10-Interest on Purchases, smc-6927-10-Interest on Purchases, syllabus-2027

Mechanics, EXT2 EQ-Bank 36

An experimental rocket is at a height of 5000 m, ascending at a speed of \(50\sqrt{2}\) m s\(^{-1}\) at an angle of 45° to the horizontal, when its engine stops. The rocket is then subject to gravity and to air resistance proportional to its velocity. Take \(g\) = 10 m s\(^{-2}\).

The velocity vector of the rocket, \(t\) seconds after the engine stops, is

\(\mathbf{v}(t) = 50e^{-0.2t}\,\mathbf{i} + (100e^{-0.2t}-50)\mathbf{j}.\)   (Do NOT prove this.)
 

  1. Show that the rocket reaches its greatest height when  \(t =5\ln 2\)  seconds, and calculate its greatest height.   (3 marks)

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  2. The pilot can only operate the ejection seat while the rocket is descending at an angle between 45° and 60° to the horizontal. Find the earliest and latest times at which the pilot can eject.   (3 marks)

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  3. As the rocket continues to fall, its speed approaches a limiting value. Find this terminal speed, justifying your answer.   (1 mark)

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a.    \(\text{See Worked Solutions}\)

b.    \(\text{Pilot can eject between 5.5 and 6.6 seconds.}\)

c.    \(\text{Terminal speed}=50 \ \text{ms}^{-1}\)

Show Worked Solution

a.    \(\mathbf{v}(t)=50 e^{-0.2 t}\,\mathbf{i}+\left(100 e^{-0.2 t}-50\right)\mathbf{j}\)

\(\text{Max height occurs when} \ \ \dot{y}=0:\)

\(100 e^{-0.2 t}-50\) \(=0\)
\(e^{-0.2 t}\) \(=\dfrac{1}{2}\)
\(-0.2 t\) \(=-\ln 2\)
\(t\) \(=5 \ln 2\)

 
\(\text{Find} \ y  \ \text{when}\ \  t=5 \ln 2:\)

\(y(t)=\displaystyle \int 100 e^{-0.2 t}-50\, d t=-500 e^{-0.2 t}-50 t+c\)

\(\text{When} \ \ t=0, y=5000:\)

\(5000=-500 e^{\circ}+c \ \Rightarrow \ c=5500\)

\(y=5500-500 e^{-0.2 t}-50 t\)
 

\(\text{At} \ \ t=5\ln 2:\)

\(y=5500-500 e^{-\ln 2}-50 \times 5 \ln 2=5076.71 \ldots=5077 \ \text{m}\).
 

b.    \(\text {On descent,} \ \ \dot{y}<0.\)

\(\text{Let} \ \ \theta=\text{angle below the horizontal}\)

\(\tan \theta=\dfrac{\abs{\dot{y}}}{\dot{x}}\)

\(\text{Let}\ \  a=e^{-0.2 t}\)

\(\tan \theta=\dfrac{50-100 a}{50 a}=\dfrac{1}{a}-2 \ \Rightarrow \ \theta=\tan ^{-1}\left(\dfrac{1}{a}-2\right)\)
 

\(\text{When} \ 45^{\circ} \ \text {is reached:}\)

\(\dfrac{1}{a}-2=1 \ \Rightarrow \ a=3\)

\(e^{-0.2 t}=\dfrac{1}{3} \ \Rightarrow \ t=\dfrac{\ln 3}{0.2} \approx 5.5 \ \text{s  (1 d.p.)}\)
 

\(\text{When} \ 60^{\circ} \ \text {is reached:}\)

\(\dfrac{1}{a}-2=\sqrt{3} \ \Rightarrow \ a=\dfrac{1}{2+\sqrt{3}}=2-\sqrt{3}\)

\(e^{-0.2 t}\) \(=2-\sqrt{3}\)
\(-0.2 t\) \(=\ln (2-\sqrt{3})\)
\(t\) \(=-5\ln (2-\sqrt{3}) \approx 6.6 \ \text{s  (1 d.p.)}\)

 
\(\therefore \ \text{Pilot can eject between 5.5 and 6.6 seconds.}\)
 

c.    \(\text{As} \ \ t \rightarrow \infty:\)

\(e^{-0.2 t} \rightarrow 0\ \ \Rightarrow\ \ \dot{x} \rightarrow 0, \ \ \dot{y} \rightarrow -50\)

\(\therefore \ \text{Terminal speed}=\sqrt{0^2+50^2}=50 \ \text{ms}^{-1}\)

Filed Under: Projectiles and Resisted Motion Tagged With: Band 4, Band 5, Band 6, smc-7442-20-Max Height, smc-7442-50-Angle of Trajectory/Impact, smc-7442-92-Vectors

Mechanics, EXT2 M1 2022 HSC 8 MC*

As a projectile of mass \(m\) kilograms travels through air, it experiences a frictional force. The magnitude of this force is proportional to the speed \(v\) of the projectile. The constant of proportionality is the positive number \(k\). The position of the particle at time \(t\) is denoted by \(\displaystyle \binom{x}{y}\). The acceleration due to gravity is  \(g \ \text{m s}^{-2}\).

Based on Newton's laws of motion, which equation models the motion of this projectile?

  1. \(\displaystyle\binom{0}{-m g}+k\binom{\dot{x}}{\dot{y}}=m\binom{\ddot{x}}{\ddot{y}}\)
  2. \(\displaystyle\binom{0}{-m g}-k\binom{\dot{x}}{\dot{y}}=m\binom{\ddot{x}}{\ddot{y}}\)
  3. \(\displaystyle\binom{0}{-m g}+k v\binom{\dot{x}}{\dot{y}}=m\binom{\ddot{x}}{\ddot{y}}\)
  4. \(\displaystyle\binom{0}{-m g}-k v\binom{\dot{x}}{\dot{y}}=m\binom{\ddot{x}}{\ddot{y}}\)
Show Answers Only

\(B\)

Show Worked Solution

\(\text{Friction} \ (F) \ \text{works against velocity}\)

\(\Rightarrow \ \text{the resistance term is subtracted (eliminate A and C)}\)
 

\(\text{Force vector has magnitude and direction.}\)

\(\text{Magnitude:} \ \ \abs{F} \propto v \ \Rightarrow \ \abs{F}=kv\ \ \ (k>0)\)

\(\text{Direction is in line with unit vector:} \ \ \dfrac{(\dot{x}, \dot{y})}{\abs{(\dot{x}, \dot{y})}}=\dfrac{(\dot{x}, \dot{y})}{v}\)
 

\(\text{Velocity vector} \ (\dot{x}, \dot{y}) \ \text{has magnitude equal to the speed:}\)

\(\abs{(\dot{x}, \dot{y})}=\sqrt{(\dot{x})^2+(\dot{y})^2}=v\)

\(\abs{-k(\dot{x}, \dot{y})}=k\abs{\dot{x}, \dot{y}}=k v\)
 

\(\text{Magnitude of resistance} \propto \text{speed}\ \  \Rightarrow\ \ -k \displaystyle\binom{\dot{x}}{\dot{y}}\ \text{(no extra}\ v \ \text{needed)}\)

\(\Rightarrow B\)

Filed Under: Projectiles and Resisted Motion Tagged With: Band 6, smc-7442-92-Vectors

Proof, EXT2 EQ-Bank 34

Consider a sequence of rectangles with side lengths \(a_{ n }\) and \(b_{ n }\).

The first rectangle has  \(a_1=2\)  and  \(b_1=1\).

For integers  \(n \geq 1,\ \ a_{n+1}=\dfrac{a_n+b_n}{2}\)  and  \(b_{n+1}=\dfrac{2}{a_{n+1}}.\)

  1. Show that every rectangle in the sequence has an area of 2 square units.   (1 mark)

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  2. Use the relationship between the arithmetic mean and the geometric mean to prove that  \(a_n \geq \sqrt{2}\)  for any integer  \(n \geq 1\).   (2 marks)

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  3. Use mathematical induction to prove that  \(a_n-\sqrt{2} \leq \dfrac{1}{2^{n-1}}(2-\sqrt{2})\)  for any integer  \(n \geq 1\).    (4 marks)

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  4. Use the squeeze theorem to show that the rectangles approach a square as \(n\) approaches infinity.   (2 marks)

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Show Worked Solution

a.    \(\text{Since}\ \ a_1 b_1=2\ \ \text{and}\ \ a_{n+1} b_{n+1}=a_{n+1} \times \dfrac{2}{a_{n+1}}=2\)

\(\Rightarrow\ \text{Each rectangle has area 2.}\)
 

b.    \(a_1=2\ \ \Rightarrow\ \ a_1 \geq \sqrt{2}\ \ \text{(true for 1st rectangle)}\)

\(\text{AM/GM inequality:}\ \ \dfrac{a_n+b_n}{2} \geq \sqrt{a_nb_n} \)

\(a_nb_n=2\ \ \text{(from part (a))}\)

\(\dfrac{a_n+b_n}{2} \geq \sqrt{2}\ …\ (1)\)

\(\text{Since}\ \ a_{n+1}=\dfrac{a_n+b_n}{2}:\)

\(\ a_{n+1} \geq \sqrt{2}\ \ \ \text{(using (1) above)}\)

\(\therefore a_n \geq \sqrt{2}\)
  

c.    \(\text{Prove}\ \ a_n-\sqrt{2} \leq \dfrac{1}{2^{n-1}}(2-\sqrt{2}),\ \ \text{for}\ \ n \geq 1\)

\(\text{If}\ \ n=1:\)

\(\ a_1-\sqrt{2}=2-\sqrt{2} \leq \dfrac{1}{2^{0}}(2-\sqrt{2})\).

\(\Rightarrow\ \text{True for}\ \ n=1.\)
 

\(\text{Assume true for}\ \ n=k:\)

\(a_k-\sqrt{2} \leq \dfrac{1}{2^{k-1}}(2-\sqrt{2})\ …\ (1) \)

\(\text{Prove true for}\ \ n=k+1:\)

\(\text{i.e.}\ \ a_{k+1}-\sqrt{2} \leq \dfrac{1}{2^k}(2-\sqrt{2})\)

\(\text{By definition,} \ \ a_{k+1}=\dfrac{1}{2}\left(a_k+b_k\right)\)

\(a_{k+1}-\sqrt{2}\) \(=\dfrac{1}{2}\left(a_k-\sqrt{2}\right)+\dfrac{1}{2}\left(b_k-\sqrt{2}\right) \)  
  \(\leq \dfrac{1}{2}\left(\dfrac{1}{2^{k-1}}(2-\sqrt{2})\right)+\dfrac{1}{2}\left(b_k-\sqrt{2}\right)\ \ \text{(see (1) above)}\ \)  

 
\(\text{Since}\ \ a_k \geq \sqrt{2}\ \ \text{and}\ \ a_kb_k=2:\)

\(\ b_k \leq \sqrt{2}\ \ \text{and}\ \ b_k-\sqrt{2} \leq 0\)

\(a_{k+1}-\sqrt{2} \leq \dfrac{1}{2^k}(2-\sqrt{2})+\dfrac{1}{2}\left(b_k-\sqrt{2}\right) \leq \dfrac{1}{2^k}(2-\sqrt{2})\)

\(\Rightarrow\ \text{True for}\ \ n=k+1.\)

\(\therefore\ \text{Since true for}\ \ n=1,\ \text{by PMI, true for integers}\ \ n \geq 1.\)
  

d.    \(\text {Combining parts (b) and (c):}\)

\(0 \leq a_n-\sqrt{2} \leq \dfrac{1}{2^{n-1}}(2-\sqrt{2}).\)

\(\text{As}\ \ n \rightarrow \infty, \ \dfrac{1}{2^{n-1}} \rightarrow 0\)

\(\Rightarrow a_n-\sqrt{2} \rightarrow 0\ \ \text{(by squeeze theorem)}\)

\(\text{Since rectangles have an area = 2:}\)

\(\text{As}\ \ n \rightarrow \infty,\ b_n \rightarrow \sqrt{2}\)

\(\text{i.e. rectangles approach a square.}\)

Filed Under: Induction, Inequalities Tagged With: Band 4, Band 5, Band 6, smc-7423-50-Arithmetic/Geometric Mean, smc-7424-10-Inequalities

Financial Maths, STD2 F1 EQ-Bank 42

Sienna buys a new car and pays a total of $2,200 in stamp duty.

Stamp duty is calculated on the vehicle as follows:

    • 3% of market value up to \(\$45\,000\)
    • 5% of market value over \(\$45\,000\)

Determine the market value of Sienna's car.   (2 marks)

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\(\$62\,000\)

Show Worked Solution

\(\text{Stamp duty on first}\ \$45\,000=0.03\times 45\,000=\$1350\)

\(\text{Remaining stamp duty}=2200-1350=\$850\)

\(\text{Amount over}\ \$45\,000=\dfrac{850}{0.05}=\$17\,000\)

\(\therefore\ \text{Market value}=45\,000+17\,000=\$62\,000\)

Filed Under: Tax and Percentage Increase/Decrease Tagged With: Band 6, smc-1125-50-Stamp Duty

Financial Maths, STD1 F1 EQ-Bank 17 MC

The total cost of a tradesperson's invoice, including 10% GST, is $462.

What was the cost of the job before GST was added?

  1. $415.80
  2. $420.00
  3. $462.00
  4. $508.20
Show Answers Only

\(B\)

Show Worked Solution

\(\text{GST-inclusive price is 110\% of original cost}\)

\(\text{Original cost}=\dfrac{462}{1.1}=\$420.00\)

\(\Rightarrow B\)

Filed Under: Tax and Percentage Increase/Decrease Tagged With: Band 6, smc-1125-20-GST

Financial Maths, STD1 F1 EQ-Bank 32

Zoe purchased a new ute for $36 000. The straight-line depreciation model used by her accountant assumes the ute decreases in value by $4800 each year.

  1. Use the straight-line depreciation formula  \(S = V_0-Dn\)  to find the salvage value of the ute after 5 years.   (1 mark)

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  2. After how many full years will the model predict the ute is worth less than $10 000?   (2 marks)

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  3. Zoe's accountant suggests that this straight-line model may not be appropriate for predicting the ute's value beyond 7 years. Give ONE reason why the model may not be suitable for long-term predictions.   (1 mark)

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Show Answers Only

a. \(\$12\,000\)

b. \(\text{After 6 full years}\)

c.    \(\text{Model limitations}\)

\(\text{Consider the expected value of the ute at}\ \ t=8:\)

\(S=36\,000-4800 \times 8=-\$2400\)

\(\text{The model predicts negative values in the long term which is unrealistic.}\)

Show Worked Solution

a.    \(\text{Find salvage value:}\)

\(S\) \(= V_0-Dn\)
  \(= 36\,000-4800 \times 5\)
  \(= \$12\,000\)

 

b.    \(\text{Find}\ n\ \text{when}\ \ S<10\,000:\)

\(S\) \(< 10\,000\)
\(36\,000-4800n\) \(< 10\,000\)
\(26\,000\) \(< 4800n\)
\(n\) \(> \dfrac{26\,000}{4800}= 5.4166…\)

 
\(\therefore\ n=6\ \text{full years}\)
 

c.    \(\text{Model limitations}\)

\(\text{Consider the expected value of the ute at}\ \ t=8:\)

\(S=36\,000-4800 \times 8=-\$2400\)

\(\text{The model predicts negative values in the long term which is unrealistic.}\)

Filed Under: Simple Interest and S/L Depreciation Tagged With: Band 5, Band 6, smc-1124-20-Straight-line Depreciation

Financial Maths, STD1 F1 2021 HSC 19 (Adapted)

Maya purchased a motorbike for $12 000. The value of the motorbike decreases according to a linear model. The graph shows the value of the motorbike, $\(V\), against the time, \(t\) months, since it was purchased.
 

  1. By how much does the value of the motorbike decrease every 10 months?   (1 mark)

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  2. Find the value of the motorbike after 4 years.   (1 mark)

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  3. Identify ONE problem with using this model to determine the value of Maya's motorbike over time.   (1 mark)

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a.     \(\$1000\)

b.     \(\$7200\)

c.     \(\text{Motorbike will have a negative value after 120 months.}\)

Show Worked Solution

a.    \(\text{Total decrease over 100 months}= 12\,000-2000= \$10\,000\)

\(\text{Decrease per 10 months}= \dfrac{10\,000}{10}= \$1000\)
 

b.    \(\text{4 years} = 4 \times 12 = 48\ \text{months}\)

\(\text{Depreciation rate}= \$100\ \text{per month}\)

\(V = 12\,000-(100 \times 48)=\$7200\)
 

c.    \(\text{Model limitations:}\)

\(\text{The linear model will eventually predict a value of \$0 (at 120 months) and negative}\)

\(\text{values beyond that, which is unrealistic.}\)

Filed Under: Simple Interest and S/L Depreciation (Std 1-X) Tagged With: adapted, Band 4, Band 6, smc-6965-20-Straight-line Depreciation

Algebra, STD1 EQ-Bank 36

Two cyclists, Aiko and Ben, are riding along the same straight track in the same direction.

Aiko starts 2000 m ahead of Ben. Aiko rides at a constant speed of 250 metres/minute and Ben rides at a constant speed of 500 metres/minute.

Let    \(d\) = distance from the starting point in metres, and 

   \(t\) = time in minutes.

  1. The equation  \(d=2000+250t\)  models Aiko's distance from the starting point.
  2. Write an equation to model Ben's distance.   (1 mark)

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  3. Use the equations from (a) to graph Aiko and Ben's journeys on the grid below.   (2 marks)

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  4. After how many minutes does Ben catch Aiko?   (1 mark)

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  5. How far has each cyclist travelled from their own starting point when they meet?   (2 marks)

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a.    \(d=500t\)

b.    

c.    \(8\ \text{minutes}\)

d.    \(\text{Aiko travelled 2000 m, Ben travelled 4000 m.}\)

Show Worked Solution

a.    \(d=500t\)

b.    \(\text{Table of values:}\)

\(\begin{array}{|c|c|c|c|c|c|c|} \hline t & 0 & 2 & 4 & 6 & 8 & 10 \\ \hline \text{Aiko} & 2000 & 2500 & 3000 & 3500 & 4000 & 4500 \\ \hline \text{Ben} & 0 & 1000 & 2000 & 3000 & 4000 & 5000 \\ \hline \end{array}\)
 

c.    \(\text{From the graph, the lines intersect at }\ t=8.\)

\(\therefore\ \text{Ben catches Aiko after 8 minutes}\)
 

d.    \(\text{When}\ \ t=8, d=4000:\)

\(\text{Aiko started 2000 m ahead, so the distance travelled}\)

\(=4000-2000=2000\ \text{m}\)

\(\text{Ben started at the origin, so the distance travelled =4000 m}\)

Filed Under: Simultaneous Linear Equations Tagged With: Band 4, Band 5, Band 6, smc-6839-20-Other SE Applications, smc-6839-30-Find Intersection

Algebra, STD1 EQ-Bank 34

Two water tanks sit side by side on a farm.

Tank A has a capacity of 1000 litres and is full. It is being emptied at a constant rate of 60 litres per minute.

At the same time, Tank B is empty and is being filled at a constant rate of 40 litres per minute.

Let    \(V\) = volume of water in litres, and 

   \(t\) = time in minutes.

  1. The equation  \(V=1000-60t\)  models the volume of water in Tank A.
  2. Write an equation to model the volume of water in Tank B.   (1 mark)

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  3. Complete the table below and use the values to graph the volume of water in Tank A and Tank B on the grid below.   (3 marks)
     
          \(\begin{array}{|c|c|c|c|c|c|c|c|} \hline t & 0 & 2 & 4 & 6 & 8 & 10 & 12 \\ \hline \text{Tank A} & \ \ \ \ \ \ \ \  & 880 & 760 & 640 & 520 & 400 & 280 \\ \hline \text{Tank B} & 0 & \ \ \ \ \ \ \ \ \  & 160 & 240 & 320 & 400 & \ \ \ \ \ \ \ \  \\ \hline \end{array}\)
  
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  1. After how many minutes do both tanks contain the same volume of water?   (1 mark)

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  2. What is the volume of water in each tank at this time?   (1 mark)

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a.    \(V=40t\)

b.    \(\text{Table of values:}\)

\(\begin{array}{|c|c|c|c|c|c|c|c|} \hline t & 0 & 2 & 4 & 6 & 8 & 10 & 12 \\ \hline \text{Tank A} & 1000 & 880 & 760 & 640 & 520 & 400 & 280 \\ \hline \text{Tank B} & 0 & 80 & 160 & 240 & 320 & 400 & 480 \\ \hline \end{array}\)

 

c.    \(10\ \text{minutes}\)

d.    \(400\ \text{litres}\)

Show Worked Solution

a.    \(V=40t\)

b.    \(\text{Table of values:}\)

\(\begin{array}{|c|c|c|c|c|c|c|c|} \hline t & 0 & 2 & 4 & 6 & 8 & 10 & 12 \\ \hline \text{Tank A} & 1000 & 880 & 760 & 640 & 520 & 400 & 280 \\ \hline \text{Tank B} & 0 & 80 & 160 & 240 & 320 & 400 & 480 \\ \hline \end{array}\)

 

c.    \(\text{From the graph, the lines intersect at }\ t=10.\)

\(\therefore\ \text{Both tanks contain the same volume after 10 minutes}\)
  

d.    \(\text{Method 1: Graphically}\)

\(\text{From the graph, when }\ t=10,\ \text{the volume in both tanks = 400 litres}\)
  

\(\text{Method 2: Algebraically}\)

\(\text{When }\ t=10:\)

\(\text{Tank A volume:}\ \ V=1000-60\times10=400\ \text{L}\)

\(\text{Tank B volume:}\ \ V=40\times10=400\ \text{L}\ \checkmark\)

\(\therefore\ \text{Each tank contains } 400\ \text{litres}\)

Filed Under: Simultaneous Linear Equations Tagged With: Band 4, Band 5, Band 6, smc-6839-20-Other SE Applications, smc-6839-30-Find Intersection

ENGINEERING, AE 2025 HSC 27c

The orthographic views of a security camera cover, manufactured from sheet metal, are shown. Complete a half pattern development of the camera cover.   (6 marks)
 

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Show Answers Only

Show Worked Solution


♦♦♦ Mean mark 34%.

Filed Under: Communication Tagged With: Band 5, Band 6, smc-3726-10-Transition pieces, smc-3726-20-Orthogonal diagrams

ENGINEERING, AE 2025 HSC 27b

Describe the process of artificial age hardening of aluminium alloys.   (3 marks)

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Show Answers Only
  • The aluminium alloy is first heated to a high temperature to create a homogeneous solid solution, then rapidly quenched to trap alloying elements in the lattice.
  • The alloy is then reheated to a moderate temperature for a controlled period.
  • This allows fine precipitate particles to form within the lattice, significantly increasing the strength and hardness of the alloy.
Show Worked Solution
  • The aluminium alloy is first heated to a high temperature to create a homogeneous solid solution, then rapidly quenched to trap alloying elements in the lattice.
  • The alloy is then reheated to a moderate temperature for a controlled period.
  • This allows fine precipitate particles to form within the lattice, significantly increasing the strength and hardness of the alloy.

♦♦♦ Mean mark 29%.

Filed Under: Materials Tagged With: Band 6, smc-3725-20-Metal alloys, smc-3725-30-Change in properties

Calculus, MET2 2025 VCAA 4

Consider the function  \(f:\left[0, \dfrac{5 \pi}{2}\right] \rightarrow R, f(x)=\sin (x)+1\).

The graph of  \(y=f(x)\)  is shown below.
 

   

  1. Evaluate  \(f\left(\dfrac{2 \pi}{3}\right)\).   (1 mark)

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  2. Find the exact values of \(x\) for which  \(f(x)=\dfrac{3}{2}\).   (1 mark)

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  3. There exist real numbers \(a\) and \(k\) in the interval \(\left(0, \dfrac{5 \pi}{2}\right)\), such that  \(f(x+k)=f(x)\) for all  \(x \in[0, a]\).
  4. Find the value of \(k\) and the largest possible value of \(a\).   (2 marks)

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  5. Consider the tangent to the graph of  \(y=f(x)\) at the point \(A\) where  \(x=\dfrac{2 \pi}{3}\), as shown on the axes below.
     

  1. Find the equation of the tangent to the graph of \(y=f(x)\) at the point where  \(x=\dfrac{2 \pi}{3}\).   (1 mark)

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  2. Apply two iterations of Newton's method to \(f\) with  \(x_0=\dfrac{2 \pi}{3}\).
    1. Write down \(x_2\), correct to one decimal place.   (1 mark)

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    2. On the axes in part d, draw the tangent to the graph of  \(y=f(x)\) at the point where  \(x=x_1\).
    3. Answer on the graph in part d.   (1 mark)

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  3. Now consider the line \(y=t(x)\), which is the tangent to the graph of  \(y=f(x)\) at the point  \((p, f(p))\), where  \(p \in\left(0, \dfrac{5 \pi}{2}\right)\).

      1. Show that  \(t(x)=\cos (p)(x-p)+\sin (p)+1\).   (2 marks)

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      2. Determine the minimum and maximum possible values for the \(y\)-intercept of  \(y=t(x)\), for  \(p \in\left(0, \dfrac{5 \pi}{2}\right)\).   (2 marks)

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      3. Determine the values of \(p\) for which  \(y=t(x)\) has a unique \(x\)-intercept that is equal to the \(x\)-intercept of  \(y=f(x)\).
      4. Give your answers correct to two decimal places.   (2 marks)

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  1. Let  \(g:\left[0, \dfrac{5 \pi}{2}\right] \rightarrow R, g(x)=a x^3+b x^2+c x+d\)  be a polynomial function, where \(a, b, c, d \in R\).
  2. Suppose  \(g(0)=f(0)\)  and  \(g^{\prime}(0)=f^{\prime}(0)\).
    1. Show that  \(c=1\)  and  \(d=1\).   (2 marks)

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    2. If  \(g(2 \pi)=f(2 \pi)\) and  \(g^{\prime}(2 \pi)=f^{\prime}(2 \pi)\), determine the area bounded by the graphs of  \(y=f(x)\)  and  \(y=g(x)\), for  \(x \in[0,2 \pi]\).
    3. Give your answer correct to two decimal places.    (2 marks)

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    4. Let  \(a=0, c=1, d=1\).
    5. Find \(b\) and \(r\), such that  \(g(r)=f(r)\) and  \(g^{\prime}(r)=f^{\prime}(r)\), where  \(b \in R\) and  \(r \in\left(0, \dfrac{5 \pi}{2}\right)\).   (2 marks)

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Show Answers Only

a.    \(f\left(\dfrac{2 \pi}{3}\right)=\dfrac{2+\sqrt{3}}{2}\)
 

b.   \(x=\dfrac{\pi}{6}, \dfrac{5 \pi}{6}, \dfrac{13 \pi}{6}\)
 

c.    \(k=2 \pi, \ \ a=\dfrac{\pi}{2}\)
 

d.    \(y=-\dfrac{x}{2}+\dfrac{\pi}{3}+\dfrac{\sqrt{3}}{2}+1\)
 

e.i.  \(x_2=5.2\)
 

e.ii.

f.i.    \(f^{\prime}(p)=\cos (p)\)

\(\text{Equation of tangent at}\ (p, \sin (p)+1):\)

\(y-(\sin (p)+1)\) \(=\cos (p)(x-p)\)
\(t(x)\) \(=\cos (p)(x-p)+\sin (p)+1\)

 

f.ii.  \(y \text{-int (min)}=1-2 \pi \ \text { (at } p=2 \pi)\)

\(y \text{-int (max)}=1+\pi \ \text { (at } p= \pi)\)
 

f.iii. \(p=2.38 \ \text{or} \ 7.04\)
 

g.i.  \(g(x)=a x^3+b x^2+c x+d, \ f(x)=\sin (x)+1\)

\(\text{Given} \ \ f(0)=g(0):\)

\(d=\sin (0)+1=1\)
 

\(g^{\prime}(x)=3 a x^2+2 b x+c, \ f^{\prime}(x)=\cos (x)\)

\(\text{Given} \ \ f^{\prime}(0)=g^{\prime}(0):\)

\(c=1\)
 

g.ii.  \(\text {Area}=1.53\)
  

g.iii. \(r=\pi, \ b=-\dfrac{1}{\pi}\)

Show Worked Solution

a.    \(f(x)=\sin (x)+1\)

\(f\left(\dfrac{2 \pi}{3}\right)=\sin \left(\dfrac{2 \pi}{3}\right)+1=\dfrac{2+\sqrt{3}}{2}\)
 

b.   \(\text{Solve \(\ f(x)=\dfrac{3}{2} \ \) for \(x\) (by CAS):}\)

\(\sin (x)+1=\dfrac{3}{2} \ \Rightarrow \ \sin (x)=\dfrac{1}{2}\)

\(\text{Solve} \ \ \sin (x)=\dfrac{1}{2} \ \text { for } \ x \in\left[0, \dfrac{5 \pi}{2}\right]:\)

\(x=\dfrac{\pi}{6}, \dfrac{5 \pi}{6}, \dfrac{13 \pi}{6}\)
 

c.    \(f(x+k)=f(x) \ \ \text{for} \ \ x \in[0, a]\)

\(\text{By inspection of graph:}\)

\(k=2 \pi, \ \ a=\dfrac{\pi}{2}\)

♦♦ Mean mark (c) 28%.

d.    \(f(x)=\sin (x)+1 \ \Rightarrow \ f^{\prime}(x)=\cos (x)\)

\(f^{\prime}\left(\dfrac{2 \pi}{3}\right)=-\dfrac{1}{2}\)

\(\text{Find equation of line} \ \ m_2=-\dfrac{1}{2} \ \ \text{through}\ \ \left(\dfrac{2 \pi}{3}, \dfrac{2+\sqrt{3}}{2}\right):\)

\(y=-\dfrac{x}{2}+\dfrac{\pi}{3}+\dfrac{\sqrt{3}}{2}+1\)
 

e.i.  \(x_0=\dfrac{2 \pi}{3}\)

\(x_1=\dfrac{2 \pi}{3}-\dfrac{f\left(\dfrac{2 \pi}{3}\right)}{f^{\prime}\left(\dfrac{2 \pi}{3}\right)}=5.8264 \ldots\)

\(x_2=5.8264 \ldots-\dfrac{f(5.8264)}{f^{\prime}(5.8264)}=5.2 \ \text{(1 d.p.)}\)
 

e.ii.

♦♦ Mean mark (e.ii) 28%.

f.i.    \(f^{\prime}(p)=\cos (p)\)

\(\text{Equation of tangent at}\ (p, \sin (p)+1):\)

\(y-(\sin (p)+1)\) \(=\cos (p)(x-p)\)
\(t(x)\) \(=\cos (p)(x-p)+\sin (p)+1\)

 

f.ii.  \(t(x)=\cos (p) x+\sin (p)+1-p \times \cos (p)\)

\(y\text{-intercept}=\sin (p)+1-p \times \cos (p)\)

\(\text{Find max/min of} \ y\text{-int for} \ p \in\left[0, \dfrac{5 \pi}{2}\right] \ \ \text{(by CAS):}\)

\(y \text{-int (min)}=1-2 \pi \ \text { (at } p=2 \pi)\)

\(y \text{-int (max)}=1+\pi \ \text { (at } p= \pi)\)

♦♦ Mean mark (f.ii) 26%.
♦♦♦ Mean mark (f.iii) 23%.

f.iii. \(x \text{-intercept of} \ f(x) \ \text{occurs at} \ \ x=\dfrac{3 \pi}{2}\)

\(\text{Solve} \ \ t\left(\dfrac{3 \pi}{2}\right)=0 \ \ \text {for}\  p:\)

\(p=2.38 \ \text{or} \ 7.04\)
 

g.i.  \(g(x)=a x^3+b x^2+c x+d, \ f(x)=\sin (x)+1\)

\(\text{Given} \ \ f(0)=g(0):\)

\(d=\sin (0)+1=1\)
 

\(g^{\prime}(x)=3 a x^2+2 b x+c, \ f^{\prime}(x)=\cos (x)\)

\(\text{Given} \ \ f^{\prime}(0)=g^{\prime}(0):\)

\(c=1\)
 

g.ii.  \(g(x)=a x^3+b x^2+x+1 \ \Rightarrow \ g^{\prime}(x)=3 a x^2+2 b x+1\)

\(\text{Given \(\ g(2 \pi)=f(2 \pi)=1\ \) and \(\ \ g^{\prime}(2 \pi)=f^{\prime}(2 \pi)=1\)}\)

\(\text{Solve \(\ g(2 \pi)=1 \ \) and \(\ g^{\prime}(2 \pi)=1\)  simultaneously for \(a, b\):}\)

\(a=\dfrac{1}{2 \pi^2}, \ b=-\dfrac{3}{2 \pi}\)

♦♦ Mean mark (g.ii) 33%.
♦♦♦ Mean mark (g.iii) 24%.

\(\text{Find intersection of}\ f(x)\ \text{and}\ g(x)\ \text{(by CAS)}:\)

\(f(x)=g(x)\ \ \Rightarrow\ \ x=\pi\)

\(\text {Area}=\displaystyle \int_0^\pi f(x)-g(x)\, d x+\int_\pi^{2 \pi} g(x)-f(x)\, d x=1.53\)
  

g.iii. \(a=0, c=1, d=1\)

\(g(x)=b x^2+x+1, \ f(x)=\sin (x)+1\)

\(g^{\prime}(x)=2 b x+1, \ f^{\prime}(x)=\cos (x)\)

\(\text{Solve simultaneous equations for \(b\) and \(r\):}\)

\(br^2+r=\sin (r)\ \ldots\ (1)\)

\(2 b r+1=\cos (r)\ \ldots\ (2)\)

\(r=\pi, \ b=-\dfrac{1}{\pi}\)

Filed Under: Area Under Curves, Tangents and Normals, Trapezium Rule and Newton, Trig Graphing Tagged With: Band 4, Band 5, Band 6, smc-2757-10-Sin, smc-5145-50-Newton's method, smc-634-30-Trig Function, smc-634-50-Find tangent given curve, smc-723-60-Trig, smc-723-80-Area between graphs

ENGINEERING, TE 2025 HSC 15 MC

A data signal and a carrier wave are combined to form the modulated signal shown.
 

What type of modulation is depicted?

  1. Amplitude modulation
  2. Frequency modulation
  3. Phase shift key modulation
  4. Frequency shift key modulation
Show Answers Only

\(D\)

Show Worked Solution
  • The data signal is digital (binary 1s and 0s) — this immediately eliminates analogue AM and FM.
  • In frequency shift key (FSK) modulation, the carrier frequency switches between two frequencies corresponding to binary 1 and 0.
  • The modulated signal shows higher frequency during the data signal high (1) and lower frequency during the low (0) — the defining characteristic of FSK.
  • Phase shift key modulation changes the phase, not the frequency — the waveform shown has no phase shifts, only frequency changes.

\(\Rightarrow D\)


♦♦♦ Mean mark 28%.

Filed Under: Electricity/Electronics Tagged With: Band 6, smc-3730-28-Analogue/Digital properties

ENGINEERING, PPT 2025 HSC 12 MC

An image of a screw jack is shown. The tommy bar is used to operate the screw jack
 

The screw jack has a pitch of 8 mm, and the force on the tommy bar is applied 400 mm from the axis of the screw.

What is the velocity ratio (VR) of the screw jack?

  1. 50
  2. 157
  3. 314
  4. 628
Show Answers Only

\(C\)

Show Worked Solution
\(VR\) \(= \dfrac{2\pi L}{p}\)  
  \(= \dfrac{2\pi \times 400}{8}\)  
  \(= \dfrac{2513.3}{8}\)  
  \(= 314\)  

  
\(\Rightarrow C\)


♦♦♦ Mean mark 24%.

Filed Under: Mechanics Tagged With: Band 6, smc-3718-20-Velocity ratio

Calculus, 2ADV C3 2025 MET2 16 MC

Consider the function  \(h(x)=a\, \log _e(b x)\), where \(a, b \in R\).

Given that its derivative \(h^{\prime}(x)\) has range \((0, \infty)\), which of the following must be true?

  1. \( a>0\)  only
  2. \( a>0\)  and  \(b<0\)
  3. \(a>0\)  and  \(b>0\)
  4. \(a b>0\)
Show Answers Only

\(D\)

Show Worked Solution

\(h(x)=a\, \log _e(b x)\)

\(h^{\prime}(x)=a\, \times \dfrac{b}{bx}=\dfrac{a}{x}\)

\(\text{Consider} \ \ h(x)=a\, \log _e(b x) \ \rightarrow \ b x>0\)
 

\(\text{Case 1:} \ \ b>0 \ \rightarrow \ x>0 \ (\text{since} \ \ b x>0 )\)

\(\dfrac{a}{x} \ \ \text{is only positive when}\ \  a>0\)
 

\(\text {Case 2:} \ \ b<0 \ \rightarrow \ x<0 \ \ (\text{since} \ \ b x>0)\)

\(\dfrac{a}{x} \ \ \text{is only positive when} \ \  a<0\)

\(\text{In both cases,} \ ab>0\)
  

\(\Rightarrow D\)

Filed Under: Interpreting and Graphing Derivatives, The Derivative Function and its Graph Tagged With: Band 6, smc-1089-50-Other, smc-7133-50-Other Problems

Calculus, MET2 2025 VCAA 19 MC

Let \(A\) be a point on the line  \(y=x+c\)  and \(B\) be a point on the curve  \(y=\log _e(x-1)\).

If \(A\) and \(B\) are placed such that the line segment \(A B\) has the minimum possible length, and this length is \(\sqrt{2}\), the value of \(c\) must be

  1. \(\sqrt{2}-2\)
  2. \(\sqrt{2}\)
  3. \(1\)
  4. \(0\)
Show Answers Only

\(D\)

Show Worked Solution

\(f(x)=x+c, \ g(x)=\log _e(x-1)\)

\(\text {Shortest distance between line and curve is perpendicular distance.}\)

\(\text{Consider the example when}\ \ c=0:\)
 

\(\text{At point \(B\), gradient \(=1\)}\)

\(\text{Solve} \ \ g^{\prime}(x)=1:\)

\(\dfrac{1}{x-1}=1 \ \Rightarrow \ x=2\)

♦♦♦ Mean mark 14%.

\(\text{Find \(\perp\) distance \((d)\) between \((2,0)\) and \((x, y)\) which lies on \(f(x)\):}\)

\(d=\sqrt{(x-2)^2+(f(x)-0)^2}=\sqrt{(x-2)^2+(x+c)^2}\)

\(\text{Minimise} \ d\ \text{(by CAS)}\ \Rightarrow \ x=\dfrac{2-c}{2}\)

\(d\left(\dfrac{2-c}{2}\right)=\sqrt{2} \ \Rightarrow \ c=0\ \ (c \neq-4)\)

\(\Rightarrow D\)

Filed Under: Maxima and Minima Tagged With: Band 6, smc-641-50-Distance

Calculus, MET2 2025 VCAA 16 MC

Consider the function  \(h(x)=a\, \log _e(b x)\), where \(a, b \in R \backslash\{0\}\).

Given that its derivative \(h^{\prime}(x)\) has range \((0, \infty)\), which of the following must be true?

  1. \( a>0\)  only
  2. \( a>0\)  and  \(b<0\)
  3. \(a>0\)  and  \(b>0\)
  4. \(a b>0\)
Show Answers Only

\(D\)

Show Worked Solution

\(h(x)=a\, \log _e(b x)\)

\(h^{\prime}(x)=a\, \times \dfrac{b}{bx}=\dfrac{a}{x}\)

\(\text{Consider} \ \ h(x)=a\, \log _e(b x) \ \Rightarrow \ b x>0\)

♦♦♦ Mean mark 18%.

\(\text{Case 1:} \ \ b>0 \ \Rightarrow \ x>0 \ (\text{since} \ \ b x>0 )\)

\(\dfrac{a}{x} \ \ \text{is only positive when}\ \  a>0\)
 

\(\text {Case 2:} \ \ b<0 \ \Rightarrow \ x<0 \ \ (\text{since} \ \ b x>0)\)

\(\dfrac{a}{x} \ \ \text{is only positive when} \ \  a<0\)

\(\text{In both cases,} \ ab>0\)

\(\Rightarrow D\)

Filed Under: The Derivative Function and its Graph Tagged With: Band 6, smc-2830-60-Other problems

ENGINEERING, PPT 2025 HSC 14 MC

An image of a shaft and its end view are shown.
 

Which drawing correctly represents section \(\text{A–A}\)?
 

 
 

Show Answers Only

\(C\)

Show Worked Solution
  • Per AS 1100, splines and shafts are not hatched in section — only the solid flange hub receives section hatching.
  • The correct section must show the central bore as an unhatched void and the spline teeth as unhatched solid features.
  • Option \(\text{C}\) correctly applies hatching only to the solid flange material, with splines and bore shown without hatching.
  • Options \(\text{A, B}\) and \(\text{D}\) incorrectly apply hatching across spline teeth or omit the correct representation of the bore.

\(\Rightarrow C\)


♦♦♦ Mean mark 25%.

Filed Under: Communication Tagged With: Band 6, smc-3721-20-Sectional views

Calculus, SPEC2 2025 VCAA 3

A tank initially contains 5 kg of salt dissolved in 3000 litres of water. Salty water that contains 0.1 kg of salt per litre of water enters the tank at a rate of 20 litres per minute. The solution is kept thoroughly mixed and drains from the tank via a tap at the same rate of 20 litres per minute.

  1. By considering concentration, explain whether the quantity of salt in the tank increases with time.   (1 mark)

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  2. Let \(Q\) denote the quantity of salt, in kilograms, in the tank at time \(t\) minutes.
  3. Show that \(Q\) satisfies the differential equation  \(\dfrac{d Q}{d t}=\dfrac{300-Q}{150}\).   (1 mark)

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  4. Using Euler's method with a step size of 15 minutes, find \(Q(30)\), the approximate quantity of salt in the tank after 30 minutes.
  5. Give your answer in kilograms, correct to two decimal places.   (2 marks)

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  6. Use calculus to solve the differential equation  \(\dfrac{d Q}{d t}=\dfrac{300-Q}{150}\), expressing \(Q\) in terms of \(t\).   (3 marks)

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  7. What value does the quantity of salt in the tank approach as time approaches infinity?
  8. Give your answer in kilograms.   (1 mark)

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  9. Find the time taken for the quantity of salt in the tank to reach 100 kg.   (1 mark)

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  10. When the quantity of salt in the tank reaches 100 kg , the tap draining the tank is turned off. Assume that the tank does not overflow and there is no change to the inflow rate.
  11. After the tap is turned off, how many minutes does it take for the concentration of salt in the tank to reach  \(\dfrac{1}{20} \ \text{kg L}^{-1}\)?   (1 mark)

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Show Answers Only

a.    \(\text{Initial concentration}=\dfrac{5}{3000}=0.001\dot{6} \ \text{kg/L}\)

\(\text{Concentration entering tank}=0.1 \ \text{kg/L}\)

\(\text{Since} \ \ 0.1>0.001\dot{6}, \ \text{salt concentration increases with time.}\)
 

b.    \(Q=\text{salt in tank at time}\  t\)

\(\dfrac{d Q}{d t}=\dfrac{d Q}{d t_{\text {in }}}-\dfrac{d Q}{d t_{\text {out }}}\)

\(\dfrac{d Q}{d t}=0.1 \times 20-\dfrac{Q}{3000} \times 20=2-\dfrac{Q}{150}=\dfrac{300-Q}{150}\)
 

c.    \(61.05 \ \text{kg}\)

d.    \(Q=300-295 e^{-\tfrac{t}{150}}\)

e.    \(\text{As} \ \ t \rightarrow \infty, Q \rightarrow 300\)

f.    \(t=150\, \log _e\left(\dfrac{59}{40}\right) \ \text {minutes }\)

g.    \(t=50 \ \text{minutes}\)

Show Worked Solution

a.    \(\text{Initial concentration}=\dfrac{5}{3000}=0.001\dot{6} \ \text{kg/L}\)

\(\text{Concentration entering tank}=0.1 \ \text{kg/L}\)

\(\text{Since} \ \ 0.1>0.001\dot{6}, \ \text{salt concentration increases with time.}\)

♦♦♦ Mean mark (a) 20%.

b.    \(Q=\text{salt in tank at time}\  t\)

\(\dfrac{d Q}{d t}=\dfrac{d Q}{d t_{\text {in }}}-\dfrac{d Q}{d t_{\text {out }}}\)

\(\dfrac{d Q}{d t}=0.1 \times 20-\dfrac{Q}{3000} \times 20=2-\dfrac{Q}{150}=\dfrac{300-Q}{150}\)
 

c.    \(Q_1=5+15 \times \dfrac{300-5}{150}=34.5 \ \text{kg}\)

\(Q_2=34.5+15 \times \dfrac{300-34.5}{150}=61.05 \ \text{kg}\)

♦ Mean mark (c) 46%.
d.     \(\dfrac{d Q}{d t}\) \(=\dfrac{300-Q}{150}\)
  \(\dfrac{d t}{d Q}\) \(=\dfrac{150}{300-Q}\)
  \(\displaystyle \int d t\) \(=\displaystyle \int \frac{150}{300-Q} d Q\)
  \( t\) \(=-150\, \log _e(300-Q)+c\)

\(\text{When} \ \ t=0, Q=5:\)

\(0=-150\, \log _e 295+c \ \ \Rightarrow \ \ c=150\, \log _e 295\)

\( t\) \(=150\, \log _e 295-150\, \log _e(300-Q)\)
\( t\) \(=150\, \log _e\left(\dfrac{295}{300-Q}\right)\)

\(\text{Solve for} \ Q \ \text{ by (CAS):}\)

\(Q=300-295 e^{-\tfrac{t}{150}}\)
 

e.    \(\text{As} \ \ t \rightarrow \infty, Q \rightarrow 300\)
 

f.    \(\text{Find \(t\) when \(Q=100\) (using part d):}\)

\(t=150\, \log _e\left(\dfrac{295}{300-100}\right)=150\, \log _e\left(\dfrac{59}{40}\right) \ \text {minutes }\)
 

g.    \(\text{After the tap is turned off:}\)

\(Q=100+0.1 \times 20 t=100+2 t\)

\(\text{Volume in tank}=3000+20 t\)

\(\text{Solve for \(t\):}\)

\(\dfrac{1}{20}=\dfrac{100+2 t}{3000+20 t}\)

\(t=50 \ \text{minutes}\)

♦♦♦ Mean mark (g) 18%.

Filed Under: Applied Contexts Tagged With: Band 4, Band 5, Band 6, smc-1184-40-Mixing problems

Vectors, SPEC1 2025 VCAA 5

The position vectors of particles \(P\) and \(Q\) at time \(t\) seconds are given by

\begin{align*}
{\underset{\sim}{r}}_P(t)=\left(t^3+a t^2\right) \underset{\sim}{i}-\underset{\sim}{j} \ \ \text {and} \ \  {\underset{\sim}{r}}_Q(t)=(b t+2 t) \underset{\sim}{i}+\left(2 t^2+c t+t\right) \underset{\sim}{j},
\end{align*}

where \(t \geq 0\)  and  \(a, b, c \in R\).

The particles collide when  \(t=1\).

  1. Show that for collision to occur when  \(t=1\), the value of \(c\) is \(-4\).   (1 mark)

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When the particles collide, their velocities are at right angles to each other.

  1. Find the two possible values of \(a\) for collision to occur when  \(t=1\).   (2 marks)

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  2. When the particles collide at  \(t=1\), the magnitudes of their accelerations are equal.
  3. Find the values of \(a\) and \(b\) for collision to occur when  \(t=1\).   (1 mark)

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Show Answers Only

a.    \(\text{\(P\) and \(Q\) collide at \(\ t=1\).}\)

\(\text{Equate co-efficients of} \ \underset{\sim}{j}:\)

\(2+c+1=-1 \ \ \Rightarrow \ \ c=-4\)

b.    \(a=-\dfrac{3}{2},-1\)

c.    \(a=-1, \ b=-2\)

Show Worked Solution

a.    \(\text{\(P\) and \(Q\) collide at \(\ t=1\).}\)

\(\text{Equate co-efficients of} \ \underset{\sim}{j}:\)

\(2+c+1=-1 \ \ \Rightarrow \ \ c=-4\)
 

b.    \(r_P=\left(t^3+a t^2\right)\underset{\sim}{i}-\underset{\sim}{j} \ \ \Rightarrow \ \ \dot{r}_P=\left(3 t^2+2 a t\right) \underset{\sim}{i}\)

\(r_Q=(b t+2 t) \underset{\sim}{i}+\left(2 t^2-3 t\right)\underset{\sim}{j} \ \ \Rightarrow \ \ \dot{r}_Q=(b+2)\underset{\sim}{i}+(4 t-3)\underset{\sim}{j}\)

\(\text {Velocities are perpendicular at} \ \ t=1:\)

\(\displaystyle \dot{r}_p \cdot \dot{r}_Q=\binom{3+2 a}{0}\binom{b+2}{1}=(3+2 a)(b+2)=0\ \ldots\ (1)\)

♦ Mean mark (b) 49%.

\(\text{Equating co-efficients of \(\underset{\sim}{i}\) at \(\ t=1\):}\)

\(1+a=b+2\)

\(\text{Substitute into (1) above:}\)

\((3+2 a)(1+a)=0\)

\(a=-\dfrac{3}{2},-1\)
 

c.    \(\ddot{r}_P=(6 t+2 a)\underset{\sim}{i}, \ \ddot{r}_Q=4 \underset{\sim}{j}\)

\(\text{At \(\ t=1\), magnitudes of \(\ddot{r}_P\) and \(\ddot{r}_Q\) are equal.}\)

\(6+2 a=4 \ \ \Rightarrow \ \ a=-1\)

\(1-1=b+2 \ \ \Rightarrow \ \ b=-2\)

♦♦♦ Mean mark (c) 25%.

Filed Under: Position Vectors as a Function of Time Tagged With: Band 2, Band 5, Band 6, smc-1178-30-Collision

Algebra, MET1 2025 VCAA 9

Consider the functions

\(f: R \backslash\{1\} \rightarrow R, f(x)=\dfrac{w^2}{(x-1)^2}\)

and

\(g: R \rightarrow R, g(x)=(x-w)^2\)

where  \(w \in R\).

  1. If  \(w=-3\), find the four solutions to  \(f(x)=g(x)\).   (3 marks)

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  2. Consider the case where  \(w>0\).
    1. Find, in terms of \(w\), the coordinates of the minimum point of the graph of  \(y=(x-1)(x-w)\).   (2 marks)

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    2. Hence, or otherwise, find the positive values of \(w\) for which \(f(x)=g(x)\) has exactly three solutions.   (2 marks)

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Show Answers Only

a.    \(\text{If} \ \ w=-3, \text{find 4 solutions to} \ \ f(x)=g(x):\)

\(\dfrac{(-3)^2}{(x-1)^2}=(x+3)^2\)

\((x+3)^2(x-1)^2=9\)

\((x+3)(x-1)= \pm 3\)
 

\(\text{Case 1}\)

\(x^2+2 x-3=3\)

\(x^2+2 x-6=0\)

\(x=-1 \pm \sqrt{7}\)
 

\(\text{Case 2}\)

\(x^2+2 x-3\) \(=-3\)
\(x(x+2)\) \(=0\)
\(x=0 \ \ \text{or} \ -2\)

 

b.i.   \(\text{Min TP at} \ \left(\dfrac{w+1}{2}, -\dfrac{1}{4} (w-1)^2\right)\)

b.ii.  \(\text{See worked solutions.}\)

Show Worked Solution

a.    \(\text{If} \ \ w=-3, \text{find 4 solutions to} \ \ f(x)=g(x):\)

\(\dfrac{(-3)^2}{(x-1)^2}=(x+3)^2\)

\((x+3)^2(x-1)^2=9\)

\((x+3)(x-1)= \pm 3\)
 

\(\text{Case 1}\)

\(x^2+2 x-3=3\)

\(x^2+2 x-6=0\)

\(x=-1 \pm \sqrt{7}\)

♦♦ Mean mark (a) 34%.

\(\text{Case 2}\)

\(x^2+2 x-3\) \(=-3\)
\(x(x+2)\) \(=0\)
\(x=0 \ \ \text{or} \ -2\)

 

b.i.  \(\text{Find minimum TP of} \ \ y=(x-1)(x-w)\)

\(\text{Axis of quadratic:}\ \ x=\dfrac{w+1}{2},\ \ (w>0)\)

\(y\) \(=\left(\dfrac{w+1}{2}-1\right)\left(\dfrac{w+1}{2}-w\right)\)
  \(=\left(\dfrac{w-1}{2}\right)\left(\dfrac{1-w}{2}\right)\)
  \(=-\dfrac{1}{4}(w-1)^2\)

 

\(\therefore \ \text{Min TP at} \ \left(\dfrac{w+1}{2}, -\dfrac{1}{4} (w-1)^2\right)\)

♦♦ Mean mark (b.i) 39%.
♦♦♦ Mean mark (b.ii) 11%.
 

b.ii.   \(\text{Solve for \(w\ (w>0)\) where \(f(x)=g(x)\):}\)

\(\dfrac{w^2}{(x-1)^2}\) \(=(x-w)^2\)
\((x-w)^2(x-1)^2\) \(=w^2\)
\([(x-w)(x-1)]^2-w^2\) \(=0\)

 

\(\text{Difference between two squares:}\)

\([(x-w)(x-1)-w][(x-w)(x-1)+w]=0\)
 

\(\text{Case 1}\)

\((x-w)(x-1)-w\) \(=0\)
\(x^2-x-w x+w-w\) \(=0\)
\(x^2-(w+1) x\) \(=0\)
\(x[x-(w+1)]\) \(=0\)

 

\(x=0 \ \ \text{or} \ \ w+1\)
 

\(\text{Case 2}\)

\((x-w)(x-1)+w\) \(=0\)
\(x^2-(w+1) x+2 w\) \(=0\)

 

\(\text{1 solution if} \ \ \Delta=0:\)

\(\Delta\) \(=[-(w+1)]^2-4 \times 1 \times 2 w\)
  \(=w^2+2 w+1-8 w\)
  \(=w^2-6 x+1\)

 

\(\text{If} \ \ \Delta=0:\)

\(w\) \(=\dfrac{6 \pm \sqrt{(-6)^2-4 \times 1 \times 1}}{2}\)
  \(=\dfrac{6 \pm \sqrt{32}}{2}\)
  \(=3+2 \sqrt{2}\ \ (\text{reject}\ w=3-2 \sqrt{2}\ \ \text{as}\ \ w>0)\)

 

\(\therefore f(x)=g(x) \ \ \text{has exactly 3 solutions}\ (w>0).\)

Filed Under: Polynomials Tagged With: Band 5, Band 6, smc-750-40-Solve Quadratic, smc-750-60-Other

Networks, GEN2 2025 VCAA 18

Frances is constructing a home gym. This project requires 12 activities, \(A\) to \(L\), to be completed.

The activity network below shows each activity and its completion time in days.
 

  1. This network contains two critical paths.
  2. State the activities that are common to both critical paths.   (1 mark)

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  3. Determine the latest start time, in days, for activity \(E\).   (1 mark)

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  4. Which activity has the longest float time?   (1 mark)

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  5. The table below shows five activities that can have their completion time reduced.
    It shows the maximum reduction time (days) and the additional cost per day, for each of the five activities.
\begin{array} {|c|c|}
\hline
\rule{0pt}{2.5ex} \ \ \textbf{Activity} \ \ & \textbf{Maximum reduction time} & \textbf{Additional cost per day }\\
\textbf{} & \textbf{(days)} \rule[-1ex]{0pt}{0pt} & \textbf{(\$) }\\
\hline
\rule{0pt}{2.5ex} \textit{A} \rule[-1ex]{0pt}{0pt} & \text{2} \rule[-1ex]{0pt}{0pt} & \text{500} \\
\hline
\rule{0pt}{2.5ex} \textit{F} \rule[-1ex]{0pt}{0pt} & \text{4} \rule[-1ex]{0pt}{0pt} & \text{150} \\
\hline
\rule{0pt}{2.5ex} \textit{G} \rule[-1ex]{0pt}{0pt} & \text{4} \rule[-1ex]{0pt}{0pt} & \text{150} \\
\hline
\rule{0pt}{2.5ex} \textit{H} \rule[-1ex]{0pt}{0pt} & \text{2} \rule[-1ex]{0pt}{0pt} & \text{300} \\
\hline
\rule{0pt}{2.5ex} \textit{K} \rule[-1ex]{0pt}{0pt} & \text{1} \rule[-1ex]{0pt}{0pt} & \text{100} \\
\hline
\end{array}
  1. Frances would like to construct the home gym in three days less than was previously possible.
  2. What is the minimum additional amount Frances will need to pay?   (1 mark)

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Show Answers Only

a.    \(\text{Critical paths: }ADHJL, ADIKL\)

b.    \(\text{LST for Activity}\ E=9 \ \text{days}\)

c.    \(\text{Activity \(F\).}\)

d.    \(\$1400\)

Show Worked Solution

a.    \(\text{Scan network forwards/backwards:}\)
  

\(\text{Critical paths: }ADHJL, ADIKL\)
 

b.    \(\text{LST for Activity}\ E\)

\(=20-4-4-3\)

\(=9 \ \text{days}\)

♦ Mean mark (a) 44%.
♦ Mean mark (b) 46%.
c.     \(\begin{array}{|l|c|c|c|c|c|}
\hline \rule{0pt}{2.5ex}\ \ \text{Activity} \ \ \rule[-1ex]{0pt}{0pt}& \ \ B \ \ &\ \ C \ \ & \ \ E \ \ & \ \ F \ \ & \ \ G \ \ \\
\hline \rule{0pt}{2.5ex} \ \ \text{Float} \ \ \rule[-1ex]{0pt}{0pt}& 5 & 1 & 5 & 6 & 1 \\
\hline
\end{array}\)

 
\(\therefore\ \text{Activity \(F\) has the longest float time.}\)

♦ Mean mark (c) 47%.

d.    \(\text{Current time = 25 days}\)

\(\text{New time = 22 days.}\)

\(\text{Reduce:} \ A(2 \ \text {days}), H(1 \ \text{day}), K(1 \ \text{day})\)

\(\text{Minimum cost}=2 \times 500+1 \times 300+1 \times 100=\$1400\)

♦♦♦ Mean mark (d) 21%.

Filed Under: Critical Path Analysis Tagged With: Band 5, Band 6, smc-621-20-Critical Paths/EST, smc-621-30-Float time/LST, smc-621-40-Crashing/Reduce completion time

Matrices, GEN2 2025 VCAA 14

An early learning centre runs seven different activities during its 40-day holiday program.

The activities are cooking \((C)\), drama \((D)\), gardening \((G)\), lunch \((L)\), music \((M)\), reading \((R)\) and sport \((S)\).

The timetabled order of the activities for day one of the holiday program is shown below.

\begin{array} {|c|c|}
\hline
\rule{0pt}{2.5ex} \ \ \text{9 am} \ \ \rule[-1ex]{0pt}{0pt} & \text{10 am} \rule[-1ex]{0pt}{0pt} & \text{11 am} \rule[-1ex]{0pt}{0pt} & \text{12 pm} \rule[-1ex]{0pt}{0pt} & \ \ \text{1 pm} \ \ \rule[-1ex]{0pt}{0pt} & \ \ \text{2 pm} \ \ \rule[-1ex]{0pt}{0pt} & \ \ \text{3 pm} \ \ \\
\hline
\rule{0pt}{2.5ex} \textit{C} \rule[-1ex]{0pt}{0pt} & \textit{D} \rule[-1ex]{0pt}{0pt} & \textit{G} \rule[-1ex]{0pt}{0pt} & \textit{L} \rule[-1ex]{0pt}{0pt} & \textit{M} \rule[-1ex]{0pt}{0pt} & \textit{R} \rule[-1ex]{0pt}{0pt} & \textit{S}\\
\hline
\end{array}

The timetabled order of the activities for day one is also shown in matrix \(X\) below.

\begin{aligned} 
X = & \begin{bmatrix}
C  \\
D \\
G \\
L \\
M \\
R\\
S \\
\end{bmatrix}
\end{aligned}

Matrix \(P\), shown below, is a permutation matrix used to determine the timetabled order of activities from one day to the next.

\begin{aligned} 
P = & \begin{bmatrix}
0 & 0 & 0 & 0 & 0 & 1 & 0 \\
0 & 0 & 0 & 0 & 0 & 0 & 1 \\
0 & 0 & 1 & 0 & 0 & 0 & 0 \\
0 & 0 & 0 & 1 & 0 & 0 & 0 \\
0 & 0 & 0 & 0 & 1 & 0 & 0 \\
0 & 1 & 0 & 0 & 0 & 0 & 0 \\
1 & 0 & 0 & 0 & 0 & 0 & 0
\end{bmatrix}
\end{aligned}

A column matrix containing the timetabled order of activities on one day is multiplied by matrix \(P\) to determine the timetabled order of activities for the next day.

  1. State the activities that are always held at the same time on each day of the program.  (1 mark)

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  2. Determine the timetabled order of the seven activities on day three of the program.  (1 mark)

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  3. \(P^4\) is an identity matrix.
  4. Explain what this means for the timetabled order of the activities over the 40-day holiday program.  (1 mark)

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Show Answers Only

a.    \(\text{Gardening, lunch, music.}\)

b.    \(\text{Drama, cooking, gardening, lunch, music, sport, reading.}\)

c.    \(\text{Order of activities rotate on a 4 day cycle.}\)

\(\text{Over 40 days, there will be 10 cycles of activities}\)

Show Worked Solution

a.    \(\text{Activities held af the same time:}\)

\(\Rightarrow \ \text{correspond to 1’s in leading diagonal}\)

\(\text{Gardening, lunch, music.}\)
 

b. 

\begin{aligned}X_2=P \times X=\begin{bmatrix}
R \\
S \\
G \\
L \\
M \\
D \\
C
\end{bmatrix}, \quad X_3=P \times X_2=\begin{bmatrix}
D \\
C \\
G \\
L \\
M \\
S \\
R
\end{bmatrix}
\end{aligned}

\(\text{Order on day 3:}\)

\(\text{Drama, cooking, gardening, lunch, music, sport, reading.}\)

♦♦ Mean mark (b) 27%.

c.    \(P^4 \ \Rightarrow \ \text{identity matrix}\)

\(\text{Order of activities rotate on a 4 day cycle.}\)

\(\text{Over 40 days, there will be 10 cycles of activities}\)

♦♦♦ Mean mark (c) 11%.

Filed Under: Matrix Applications Tagged With: Band 4, Band 5, Band 6, smc-619-40-Interpret Elements, smc-619-90-Permutation

Matrices, GEN2 2025 VCAA 13

An early learning centre offers a 10-week activity program for four-year-old children. There are 27 children enrolled in the program. They participate in three different activities over the 10 weeks. The activities are cooking \((C)\), gardening \((G)\) and music \((M)\).

The transition matrix \(K\), shown below, gives the expected proportion of children in the program who will change activities from one week to the next.

\begin{aligned}
& \quad \quad \ \ \ \textit{this week} \\
& \quad  \ \ C \quad \quad G \ \quad \ \ M \\
K = & \begin{bmatrix}
0  & 0.76   & 0.36 \\
0.55  & 0  & 0.64 \\
0.45  & 0.24  & 0\\
\end{bmatrix}\begin{array}{l}
C\\
G\\
M
\end{array} \ \textit{next week} \\
\end{aligned}

  1. What do the values on the leading diagonal in matrix \(K\) indicate?   (1 mark)

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  2. In Week 1 of the program, all 27 children participate in cooking \((C)\).
    1. Calculate the expected percentage of children who will participate in cooking in Week 10 of the program. Round your answer to one decimal place.   (1 mark)

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    2. Find the expected number of children who will participate in gardening \((G)\) in Week 3 of the program and then move across to music \((M)\) in Week 4 of the program. Round your answer to the nearest whole number.   (2 marks)

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Show Answers Only

a.    \(\text{No child does the same activity in two consecutive weeks.}\)

b.i.  \(37.4\%\)

b.ii. \(2 \ \text{children}\)

Show Worked Solution

a.    \(\text{Leading diagonal made up of 0’s:}\)

\(\text{No child does the same activity in two consecutive weeks.}\)
 

b.i.  \(\text{Find number of children cooking in week 10:}\)

\begin{aligned}K^9\begin{bmatrix}
27 \\
0 \\
0
\end{bmatrix}=\begin{bmatrix}
10.08 \ldots\\
9.96 \ldots \\
6.94 \ldots
\end{bmatrix}
\end{aligned}

\(\text{% children cooking}=\dfrac{10.08 \ldots}{27} \times 100=37.35 \ldots=37.4\% \ \text{(1 d.p.)}\)

♦♦♦ Mean mark (b.i) 9%.

b.ii.  \(\text{At the start of week 3:}\)

\begin{aligned}K^2\begin{bmatrix}
27 \\
0 \\
0
\end{bmatrix}=\begin{bmatrix}
15.66 \\
7.776 \\
3.564
\end{bmatrix}
\end{aligned}

\(\text{Children who move from \(G\) (week 3) to \(M\) (week 4)}\)

\(=7.776 \times 0.24=1.886 \ldots=2 \ \text{children}\)

♦♦♦ Mean mark (b.ii) 21%.

Filed Under: Transition Matrices - Regular Tagged With: Band 4, Band 6, smc-618-24-Interpret Matrix, smc-618-61-3x3 Matrix

Matrices, GEN2 2025 VCAA 12

The early learning centre contains three rooms, Nursery \((N)\), Toddler \((T)\) and Pre-kinder \((P)\) .

From one year to the next, children can move between rooms, stay in the same room, or may leave \((L)\) the centre. The following transition matrix, \(M\), shows the expected proportion of children who will move between categories or stay in the same category from one year to the next.

\begin{aligned}
& \quad \quad \quad  \quad \quad \textit{this year} \\
& \quad \quad \ \ \ \ N \quad \quad \ \  T \quad \quad P \quad \  L \\
M&=\begin{bmatrix}
0.25 & 0 & 0 & 0 \\
0.625 & 0.25 & 0 & 0 \\
0 & 0.625 & 0.1 & 0 \\
0.125 & 0.125 & 0.9 & 1
\end{bmatrix}\begin{array}{l}
N\\
T \\
P \\
P
\end{array}\quad \textit{next year}
\end{aligned}

  1. The number of children expected to be in each of the four categories, from one year to the next, can be calculated using the matrix recurrence relation
    1. \(S_{n+1}=M S_n\)
  2. where \(S_n\) represents the expected number of children in each of the four categories at the start of year \(n\).
  3. The state matrix \(S_{2024}\), shown below, gives the number of children in each category at the start of 2024.
      1. \begin{align*}S_{2024}=\left[\begin{array}{c}4 \\15 \\15 \\27\end{array}\right]\begin{aligned}& N \\& T \\& P \\& L\end{aligned}\end{align*}
  4. Find \(S_{2023}\).   (1 mark)

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  5. From the start of 2025, new children commenced in the early learning centre at the start of each year.
  6. A new matrix recurrence relation for determining the expected number of children in each of the four categories from one year to the next is
      1. \begin{align*}
        S_{n+1}=M S_n+B
        \end{align*}
  7. where
      1. \begin{align*}B=\left[\begin{array}{c}12 \\5 \\10 \\0\end{array}\right] \begin{aligned}& N \\& T \\& P \\& L\end{aligned}\end{align*}
  8. gives the number of new children enrolled in each room of the early learning centre at the start of each year.
  9. Given the state matrix
    1. \begin{align*}S_{2024}=\left[\begin{array}{c}4 \\15 \\15 \\27\end{array}\right]\begin{aligned}& N \\& T \\& P \\& L\end{aligned}\end{align*}
  10. find the expected total number of children to be enrolled in the early learning centre at the start of 2026. Round your answer to the nearest whole number.   (1 mark)

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a.   

\(S_{2023}=\begin{bmatrix}16 \\ 20 \\ 25 \\ 0\end{bmatrix}\)

b.    \(\text{Children enrolled (2026) =50}\)

Show Worked Solution

a.    \(S_{n+1}=M S_n \ \Rightarrow \ S_n=M^{-1} S_{n+1}\)

\(S_{2023}=\begin{bmatrix}0.25 & 0 & 0 & 0 \\ 0.625 & 0.25 & 0 & 0 \\ 0 & 0.625 & 0.1 & 0 \\ 0.125 & 0.125 & 0.9 & 1\end{bmatrix}^{-1}\begin{bmatrix}4 \\ 15 \\ 15 \\ 27\end{bmatrix}=\begin{bmatrix}16 \\ 20 \\ 25 \\ 0\end{bmatrix}\)

♦ Mean mark (a) 53%.

b.

\(S_{2025}=M S_{2024} + B=\begin{bmatrix}13 \\ 11.25 \\ 20.87 \\ 42.87\end{bmatrix}\)
 

\(S_{2026}=M S_{2025} + B=\begin{bmatrix}15.25 \\ 15.93 \\ 19.11 \\ 64.69\end{bmatrix}\)
 

\(\text{Children enrolled (2026)\(=15.25+15.93+19.11=50\) (nearest whole)}\)

♦♦♦ Mean mark (b) 13%.

Filed Under: Transition Matrices - Modified Tagged With: Band 5, Band 6, smc-1893-20-State Matrix in discrete period, smc-1893-32-4x4 Matrix

Financial Maths, GEN2 2025 VCAA 10

Using profits from his recent film, Declan invests $650 000 into a 10-year annuity.

The annuity earns interest at 6.4% per annum, compounding quarterly.

Declan receives a regular quarterly payment from the annuity.

Halfway through the 10-year annuity, Declan writes a recurrence relation to represent the quarter-to-quarter balance for the remainder of the annuity.

Let \(D_n\) be the balance of Declan's annuity \(n\) quarters after the halfway point of the annuity.

Complete the recurrence relation below in terms of \(D_0, D_{n+1}\) and \(D_n\) that can model this balance.   (2 marks)

  \(D_0=\begin{array}{|c|}\hline \rule{0pt}{4ex}  \quad \quad \quad \quad \quad & \quad \quad \quad \quad \quad \\ \hline \end{array}, D_{n+1}=1.016 \times D_n+\begin{array}{|c|}\hline \rule{0pt}{4ex}  \quad \quad \quad \quad \quad & \quad \quad \quad \quad \quad \\ \hline \end{array}\)

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\(D_0=376\,159.43, D_{n+1}=1.016 \times D_n-22\,126.27\)

Show Worked Solution

\(\text{Find annuity quarterly payment.}\)

\(\text{Solve for \(PMT\) (by CAS):}\)

\(N\) \(=40\)
\(I(\%)\) \(=6.4\)
\(PV\) \(=-650\,000\)
\(PMT\) \(=\boldsymbol{22\,126.27}\)
\(FV\) \(=0\)
\(PY\) \(=CY=4\)
♦♦♦ Mean mark 17%.

\(\text{Find annuity balance at halfway:}\)

\(\text{Solve for \(FV\) (by CAS):}\)

\(N\) \(=20\)
\(I(\%)\) \(=6.4\)
\(PV\) \(=-650\,000\)
\(PMT\) \(=22\,126.27\)
\(FV\) \(=\boldsymbol{376\,159.428}\)
\(PY\) \(=CY=4\)

 

\(\text{Recurrence relation:}\)

\(D_0=376\,159.43, D_{n+1}=1.016 \times D_n-22\,126.27\)

Filed Under: Annuities and Perpetuities Tagged With: Band 6, smc-2512-10-Annuity, smc-2512-50-CAS solver

Financial Maths, GEN2 2025 VCAA 7

Declan is a filmmaker and content creator.

He has taken out a reducing balance loan to fund a new production.

Interest is calculated monthly and Declan makes monthly repayments.

Three rows of the amortisation table for Declan’s loan are shown below.

\begin{array}{|c|c|c|c|c|}
\hline
\hline \rule{0pt}{2.5ex}\quad \textbf{Payment} \quad & \quad\textbf{Payment} \quad & \quad\textbf{Interest} \quad& \textbf{Principal} & \quad\textbf{Balance}\quad\\
\textbf{number} & \textbf{(\$)}  \rule[-1ex]{0pt}{0pt}& \textbf{(\$)} & \quad\textbf{reduction (\$)} \quad& \textbf{(\$)}\\
\hline \hline \rule{0pt}{2.5ex}0 \rule[-1ex]{0pt}{0pt}& 0.00 & 0.00 & 0.00 & 850\,000.00 \\
\hline \hline \rule{0pt}{2.5ex}1\rule[-1ex]{0pt}{0pt} & 15\,730.88 & 2975.00 & 12\,755.88 & 837\,244.12 \\
\hline \hline \rule{0pt}{2.5ex}2 \rule[-1ex]{0pt}{0pt}& 15\,730.88 & 2930.35 & 12\,800.53 & 824\,443.59 \\
\hline
\end{array}

  1. What amount, in dollars, did Declan borrow?   (1 mark)

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  2. Why is the interest associated with payment 2 lower than the interest associated with payment 1?   (1 mark)

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  3. The interest rate on Declan’s loan is 4.2% per annum, compounding monthly.
  4. Using the values in the table, complete the table below.
  5. Round all values to the nearest cent.   (1 mark)

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\begin{array}{|c|c|c|c|c|}
\hline
\hline \rule{0pt}{2.5ex}\quad \textbf{Payment} \quad & \quad\textbf{Payment} \quad & \quad\textbf{Interest} \quad& \textbf{Principal} & \quad\textbf{Balance}\quad\\
\textbf{number} & \textbf{(\$)}  \rule[-1ex]{0pt}{0pt}& \textbf{(\$)} & \quad\textbf{reduction (\$)} \quad& \textbf{(\$)}\\
\hline \hline \rule{0pt}{2.5ex}0 \rule[-1ex]{0pt}{0pt}& 0.00 & 0.00 & 0.00 & 850\,000.00 \\
\hline \hline \rule{0pt}{2.5ex}1\rule[-1ex]{0pt}{0pt} & 15\,730.88 & 2975.00 & 12\,755.88 & 837\,244.12 \\
\hline \hline \rule{0pt}{2.5ex}2 \rule[-1ex]{0pt}{0pt}& 15\,730.88 & 2930.35 & 12\,800.53 & 824\,443.59 \\
\hline \hline \rule{0pt}{2.5ex}3 \rule[-1ex]{0pt}{0pt}& 15\,730.88 & & & \\
\hline
\end{array}

  1. The last payment required to fully repay the loan is $15 730.71, correct to the nearest cent.
  2. How many payments of $15 730.88 did Declan make before this final payment?   (1 mark)

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a.    \(\$ 850\,000\)

b.    \(\text{Interest is lower (payment 2 vs payment 1) because it is based on}\)

\(\text{a reduced balance.}\)

c.    \(\text{Interest}=\dfrac{4.2}{100} \times \dfrac{1}{12} \times 824\, 443.59=\$ 2885.55\)

\(\text{Principal reduction}=15\,730.88-2885.55=\$ 12\,845.33\)

\(\text{Balance}=824\,443.59-12\,845.33=\$811\,598.26\)

d.    \(\text{59 payments made before the final payment.}\)

Show Worked Solution

a.    \(\$ 850\,000\)
 

b.    \(\text{Interest is lower (payment 2 vs payment 1) because it is based on}\)

\(\text{a reduced balance.}\)
 

c.    \(\text{Interest}=\dfrac{4.2}{100} \times \dfrac{1}{12} \times 824\, 443.59=\$ 2885.55\)

\(\text{Principal reduction}=15\,730.88-2885.55=\$ 12\,845.33\)

\(\text{Balance}=824\,443.59-12\,845.33=\$811\,598.26\)

♦ Mean mark (c) 40%.

d.    \(\text{Solve for \(N\) (by CAS):}\)

\(N\) \(=\boldsymbol{59.99 \ldots}\)
\(I(\%)\) \(=4.2\)
\(PV\) \(=850\,000\)
\(PMT\) \(=-15\,730.88\)
\(FV\) \(=0\)
\(PY\) \(=CY=12\)

 
\(\therefore \ \text{59 payments made before the final payment.}\)

♦♦♦ Mean mark (d) 21%.

Filed Under: Borrowing and Loans Tagged With: Band 4, Band 5, Band 6, smc-603-50-\(P+I-R\) tables, smc-603-60-CAS (1 step)

Data Analysis, GEN2 2025 VCAA 6

The time series plot below shows the number of homes sold in a town each month over a four‑year period.

Month 1 is January 2016 and month 48 is December 2019.
 

  1. Excluding any possible outliers, identify two qualitative features of the time series plot.   (2 marks)

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  2. The total number of sales in each of the four years is given in the table below.

\begin{array}{|c|c|}
\hline \rule{0pt}{2.5ex}\quad \textbf{Year} \quad \rule[-1ex]{0pt}{0pt}& \textbf{Total number of sales}\\
\hline \rule{0pt}{2.5ex}2016 \rule[-1ex]{0pt}{0pt}& 361 \\
\hline \rule{0pt}{2.5ex}2017 \rule[-1ex]{0pt}{0pt}& 354 \\
\hline \rule{0pt}{2.5ex}2018 \rule[-1ex]{0pt}{0pt}& 358 \\
\hline \rule{0pt}{2.5ex}2019 \rule[-1ex]{0pt}{0pt}& 357 \\
\hline
\end{array}

  1. A seasonal index can be calculated for each month based on the four-year period.
  2. Calculate this seasonal index for September, the ninth month in the calendar year. Round your answer to three decimal places.   (2 marks)

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a.    \(\text{Seasonality, irregular fluctuations.}\)

b.    \(\text{Seasonal index(Sep)} =0.587\)

Show Worked Solution

a.    \(\text{Qualitative features of time series plot:}\)

\(\text{Seasonality}\)

\(\text{Irregular fluctuations}\)
 

b.    \(\text{Sept avg}=\dfrac{15+20+20+15}{4}=17.5\)

\(\text {Monthly avg}=\dfrac{361+354+358+357}{48}=29.79 \ldots\)

\(\text{Seasonal index (Sep)}=\dfrac{17.5}{29.79 \ldots}=0.5874 \ldots=0.587\ \text{(3 d.p.)}\)

Filed Under: Time Series Tagged With: Band 4, Band 6, smc-266-10-Seasonal Index from a Table, smc-266-40-Time Series Trends

Data Analysis, GEN2 2025 VCAA 4

The scatterplot below shows the sale price of a home, in dollars, against the distance of the home from the city centre of Melbourne, in kilometres, distance from city centre.

The sample consists of three‑bedroom homes sold between 2016 and 2018
 

The equation of the least squares line for the data in the scatterplot is

sale price\(=1\,765\,353-35\,054 \times\)distance from city centre

The coefficient of determination is 0.0806

  1. Identify the explanatory variable in the least squares equation.   (1 mark)

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  2. Calculate the value of the correlation coefficient \(r\). Round your answer to three decimal places.   (1 mark)

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  3. Use the equation of the least squares line to predict the sale price for a three-bedroom home, located in the city centre of Melbourne, sold between 2016 and 2018.   (1 mark)

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  4. Jocelyn wants to sell her three-bedroom home located two kilometres from the city centre of Melbourne.
  5. Would the predicted sale price be an example of interpolation or extrapolation?
  6. Briefly explain your answer.   (1 mark)

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  7. Describe the linear association between sale price and distance from city centre in terms of its strength and direction. Answer in the table below.  (2 marks)

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\begin{array}{|l|l|}
\hline \rule{0pt}{2.5ex}\text {strength} \quad \quad \rule[-1ex]{0pt}{0pt}& \quad \quad \quad \quad \quad \quad  \quad \quad \quad \quad \quad \quad \\
\hline \rule{0pt}{2.5ex}\text {direction} \rule[-1ex]{0pt}{0pt}& \\
\hline
\end{array}

  1. A residual plot associated with the least squares line is shown below.
  2. It is missing one point.
     

  1. The residual associated with the home that is furthest from the city centre of Melbourne is missing from the residual plot. The home is 15.5 km from the city centre and sold for $1 250 000.
    1. Show that the value of the missing residual is 27 984.   (1 mark)

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    2. Plot the residual from part i by placing an \(\text{X}\) on the residual plot above.   (1 mark)

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a.    \(\text{Distance from city centre}\)

b.   \(r=-0.284\)

c.    \(\text{sale price}=1\,765\,353\)

d.    \(\text{Extrapolation as 2 km lies outside the explanatory variable data range.}\)

e.    \(\text{Strength: weak. Direction: negative}\)

f.i.  \(\text{Sale price (est)}=1\,765\,353-35\,054 \times 15.5=1\,222\,016\)

\(\text{Actual sale price}=1\,250\,000\)

\(\text{Residual}=1\,250\,000-1\,222\,016=27\,984\)

f.ii.

       

Show Worked Solution

a.    \(\text{Distance from city centre}\)
 

b.   \(\text{Since slope is negative}\)

\(r=-\sqrt{0.0806}=-0.284\)

♦♦♦ Mean mark (b) 21%.

c.    \(\text{Find sale price when distance fran city centre}=0:\)

\(\text{sale price}=1\,765\,353\)
 

d.    \(\text{Extrapolation as 2 km lies outside the explanatory variable data range.}\)

\(\text{(Note: interpolation/extrapolation should be referenced to the}\)

\(\text{explanatory variable range).}\)

♦♦ Mean mark (d) 27%.

e.    \(\text{Strength: weak}\)

\(\text{Direction: negative}\)
 

f.i.  \(\text{Sale price (est)}=1\,765\,353-35\,054 \times 15.5=1\,222\,016\)

\(\text{Actual sale price}=1\,250\,000\)

\(\text{Residual}=1\,250\,000-1\,222\,016=27\,984\)

♦ Mean mark (f.i) 41%.
♦ Mean mark (f.ii) 45%

f.ii.

       

Filed Under: Correlation and Regression Tagged With: Band 4, Band 5, Band 6, smc-265-10-r / r^2 and Association, smc-265-50-Residuals, smc-265-60-Extrapolation / Interpolation

HMS, TIP 2025 HSC 26

Analyse the relationship between training thresholds and TWO physiological adaptations. In your answer, provide examples of both aerobic and resistance training.  (8 marks)

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Overview Statement:

  • Training thresholds represent critical intensity levels that trigger specific physiological adaptations.
  • Understanding how aerobic and resistance thresholds connect to metabolic and muscular changes can open up pathways to enhanced athletic performance.

Aerobic Threshold and Cardiovascular Adaptations:

  • The aerobic training threshold occurs at approximately 70% of maximum heart rate. Training at this intensity influences fuel utilisation and cardiovascular function.
  • This causes the body to shift from primarily using fat to using carbohydrates for energy. For example, a marathon runner training at 70% max heart rate stimulates this metabolic adaptation.
  • The threshold also triggers increased stroke volume through enhanced left ventricle filling capacity. This relationship results in improved cardiac output and oxygen delivery to working muscles.
  • Consequently, athletes sustain effort over extended periods with greater efficiency. This shows that aerobic threshold training enables both metabolic and cardiovascular improvements for endurance performance.

Resistance Threshold and Muscular Adaptations:

  • Resistance training thresholds involve working at 70-85% of one-rep maximum with 6-12 repetitions. This intensity creates sufficient mechanical stress to stimulate muscle hypertrophy.
  • For instance, a weightlifter performing squats at 80% of 1RM bmicroscopic muscle fibre damage. This initiates increased protein synthesis and muscle repair processes.
  • The threshold works through progressive overload that leads to enlarged muscle fibres with increased actin and myosin filaments. As a result, greater force production capacity develops.
  • The significance is that athletes gain strength and power output essential for explosive movements.

Implications and Synthesis:

  • These thresholds work together as intensity markers that determine adaptation type. Aerobic thresholds influence metabolic and cardiovascular systems whilst resistance thresholds affect muscular structure.
  • Therefore, coaches must apply appropriate threshold intensities to achieve specific performance goals. This reveals that training success depends on understanding the precise relationship between intensity levels and resulting physiological changes.
Show Worked Solution

Overview Statement:

  • Training thresholds represent critical intensity levels that trigger specific physiological adaptations.
  • Understanding how aerobic and resistance thresholds connect to metabolic and muscular changes can open up pathways to enhanced athletic performance.

Aerobic Threshold and Cardiovascular Adaptations:

  • The aerobic training threshold occurs at approximately 70% of maximum heart rate. Training at this intensity influences fuel utilisation and cardiovascular function.
  • This causes the body to shift from primarily using carbohydrate to using fat for energy. For example, a marathon runner training at 70% max heart rate stimulates this metabolic adaptation.
  • The threshold also triggers increased stroke volume through enhanced left ventricle filling capacity. This relationship results in improved cardiac output and oxygen delivery to working muscles.
  • Consequently, athletes sustain effort over extended periods with greater efficiency. This shows that aerobic threshold training enables both metabolic and cardiovascular improvements for endurance performance.

Resistance Threshold and Muscular Adaptations:

  • Resistance training thresholds involve working at 70-85% of one-rep maximum with 6-12 repetitions. This intensity creates sufficient mechanical stress to stimulate muscle hypertrophy.
  • For instance, a weightlifter performing squats at 80% of 1 repetition maximum causes microscopic damage to the muscle fibres. This initiates increased protein synthesis and muscle repair processes.
  • The threshold works through progressive overload that leads to enlarged muscle fibres with increased actin and myosin filaments. As a result, greater force production capacity develops.
  • The significance is that athletes gain strength and power output essential for explosive movements.

Implications and Synthesis:

  • These thresholds work together as intensity markers that determine adaptation type. Aerobic thresholds influence metabolic and cardiovascular systems whilst resistance thresholds affect muscular structure.
  • Therefore, coaches must apply appropriate threshold intensities to achieve specific performance goals. This reveals that training success depends on understanding the precise relationship between intensity levels and resulting physiological changes.

♦♦ Mean mark 36%.

Filed Under: Physiological adaptations and improved performance Tagged With: Band 4, Band 5, Band 6, smc-5461-10-Cardiorespiratory, smc-5461-20-Muscular

CHEMISTRY, M6 2025 HSC 34

A 0.010 L aliquot of an acid was titrated with 0.10 mol L\(^{-1} \ \ce{NaOH}\), resulting in the following titration curve.
 

  1. Calculate the \(K_a\) for the acid used.   (3 marks)

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  2. The concentration of the \(\ce{NaOH}\) was 0.10 mol L\(^{-1}\).
  3. Explain why the pH of the final solution never reached 13.   (2 marks)
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a.   \(\text{Strategy 1:}\)
 

\(\text{From the shape of the titration curve, the acid was weak.}\)

\(\text{Equivalence point}\ \ \Rightarrow \ \ \ce{NaOH}\ \text{added}\ = 0.24\ \text{L} \)

\(\text{Halfway to the equivalent point = 0.012 L}, \ce{[ HA ]=\left[ A^{-}\right]}\)

\(\text{Here the pH} \approx 4.4 , \text{or}\ \ce{\left[H^{+}\right] is 4.0 \times 10^{-5}}\).

\(K_a=10^{-\text{pH}}=\ce{\left[H+\right]} \times \dfrac{\ce{\left[A^{-}\right]}}{\ce{[HA]}}\)

\(\text{At this pH,} \ \ce{\left[A^{-}\right]=[HA] so} \ K_a=4.0 \times 10^{-5}\).
 

\(\text{Strategy 2:}\)

\(\text{Equivalence point is at} \ \ce{0.024 L NaOH added}\).

\(\text{Shape of curve shows acid is monoprotic.}\)

\(\ce{[HA] \times 0.010=0.1 \times 0.024}\)

\(\ce{[HA]=0.24 mol L^{-1}}\)

\(\text{pH at start is approximately 2.5}\)

\(\text{So,} \ \ce{\left[H+\right]=3.16 \times 10^{-3}}\)

\(K_a=\dfrac{\ce{\left[H^{+}\right]\left[A^{-}\right]}}{\ce{[HA]}} \quad \ce{\left[A^{-}\right]=\left[H^{+}\right]}\)

\(\ce{[HA]=0.24-3.16 \times 10^{-3}=0.237}\)

\(K_a=\dfrac{\left(3.16 \times 10^{-3}\right)^2}{0.237}=4.2 \times 10^{-5}\)
 

b.   pH of the final solution < 13:

  • Some of the hydroxide was neutralised by the acid.
  • The 10 mL of acid also diluted the NaOH.
  • So the \(\ce{NaOH}\) concentration of the mixture will be less than 0.1 mol L\(^{-1}\) and the pH will be less than 13.
Show Worked Solution

a.   \(\text{Strategy 1:}\)
 

♦♦ Mean mark 40%.

\(\text{From the shape of the titration curve, the acid was weak.}\)

\(\text{Equivalence point}\ \ \Rightarrow \ \ \ce{NaOH}\ \text{added}\ = 0.24\ \text{L} \)

\(\text{Halfway to the equivalent point = 0.012 L}, \ce{[ HA ]=\left[ A^{-}\right]}\)

\(\text{Here the pH} \approx 4.4 , \text{or}\ \ce{\left[H^{+}\right] is 4.0 \times 10^{-5}}\).

\(K_a=10^{-\text{pH}}=\ce{\left[H+\right]} \times \dfrac{\ce{\left[A^{-}\right]}}{\ce{[HA]}}\)

\(\text{At this pH,} \ \ce{\left[A^{-}\right]=[HA] so} \ K_a=4.0 \times 10^{-5}\).
 

\(\text{Strategy 2:}\)

\(\text{Equivalence point is at} \ \ce{0.024 L NaOH added}\).

\(\text{Shape of curve shows acid is monoprotic.}\)

\(\ce{[HA] \times 0.010=0.1 \times 0.024}\)

\(\ce{[HA]=0.24 mol L^{-1}}\)

\(\text{pH at start is approximately 2.5}\)

\(\text{So,} \ \ce{\left[H+\right]=3.16 \times 10^{-3}}\)

\(K_a=\dfrac{\ce{\left[H^{+}\right]\left[A^{-}\right]}}{\ce{[HA]}} \quad \ce{\left[A^{-}\right]=\left[H^{+}\right]}\)

\(\ce{[HA]=0.24-3.16 \times 10^{-3}=0.237}\)

\(K_a=\dfrac{\left(3.16 \times 10^{-3}\right)^2}{0.237}=4.2 \times 10^{-5}\)
 

b.   pH of the final solution < 13:

  • Some of the hydroxide was neutralised by the acid.
  • The 10 mL of acid also diluted the NaOH.
  • So the \(\ce{NaOH}\) concentration of the mixture will be less than 0.1 mol L\(^{-1}\) and the pH will be less than 13.
♦♦♦ Mean mark 19%.

Filed Under: Quantitative Analysis Tagged With: Band 5, Band 6, smc-3675-20-Titration Curves and Conductivity Graphs, smc-3675-30-Ka/Kb

CHEMISTRY, M5 2025 HSC 32

The following three solids were added together to 1 litre of water:

  • \(\ce{0.006\ \text{mol}\ Mg(NO3)2}\)
  • \(\ce{0.010\ \text{mol}\ NaOH}\)
  • \(\ce{0.002\ \text{mol}\ Na2CO3}\).

Which precipitate(s), if any, will form? Justify your answer with appropriate calculations.   (5 marks)

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All sodium and nitrate salts are soluble  \(\Rightarrow\)  possible precipitates are \(\ce{Mg(OH)2}\) and \(\ce{MgCO3}\). 

\(\ce{\left[Mg^{2+}\right]=6 \times 10^{-3} \quad\left[ OH^{-}\right]=1 \times 10^{-2} \quad\left[ CO3^{2-}\right]=2 \times 10^{-3}}\)

\(\ce{\left[Mg^{2+}\right]\left[ OH^{-}\right]^2=6 \times 10^{-7} \quad \quad \quad \ \ \ K_{\textit{sp}}=5.61 \times 10^{-12}}\)

\(\ce{\left[ Mg^{2+}\right]\left[ CO3^{2-}\right]=1.2 \times 10^{-5} \quad \quad  K_{\textit{sp}}=6.82 \times 10^{-6}}\)
 

\(\ce{Mg(OH)2}\) is a lot less soluble than \(\ce{MgCO3}\) and will precipitate preferentially.

\(\ce{\left[Mg^{2+}\right]\left[OH^{-}\right]^2 > K_{\textit{sp}}}\)

\(\Rightarrow \ce{Mg(OH)2}\) will precipitate.
 

\(\ce{Mg^{2+}(aq) + 2OH-(aq) \rightarrow Mg(OH)2(s)}\)

Since \(K_{\textit{sp}}\) is small, assume reaction goes to completion.

\(\ce{n(Mg^{2+})=0.006\ mol, n(OH^{-})=0.010\ mol}\)

Using stoichiometric ratio \((1:2)\)

\(0.006 > \dfrac{0.010}{2}=0.005\ \ \Rightarrow \ce{Mg^{2+}}\) is in excess.

Concentration drops to: \(6 \times 10^{-3}-5 \times 10^{-3}=1 \times 10^{-3}\).
 

Check if \(\ce{MgCO3}\) will precipitate:

\(\ce{\left[Mg^{2+}\right]\left[CO3^{2-}\right]}\) becomes  \(2 \times 10^{-6} <K_{\textit{sp}}\).

\(\ce{\Rightarrow\ MgCO3}\) won’t precipitate.

Show Worked Solution

All sodium and nitrate salts are soluble  \(\Rightarrow\)  possible precipitates are \(\ce{Mg(OH)2}\) and \(\ce{MgCO3}\). 

\(\ce{\left[Mg^{2+}\right]=6 \times 10^{-3} \quad\left[ OH^{-}\right]=1 \times 10^{-2} \quad\left[ CO3^{2-}\right]=2 \times 10^{-3}}\)

\(\ce{\left[Mg^{2+}\right]\left[ OH^{-}\right]^2=6 \times 10^{-7} \quad \quad \quad \ \ \ K_{\textit{sp}}=5.61 \times 10^{-12}}\)

\(\ce{\left[ Mg^{2+}\right]\left[ CO3^{2-}\right]=1.2 \times 10^{-5} \quad \quad  K_{\textit{sp}}=6.82 \times 10^{-6}}\)

♦♦ Mean mark 40%.

\(\ce{Mg(OH)2}\) is a lot less soluble than \(\ce{MgCO3}\) and will precipitate preferentially.

\(\ce{\left[Mg^{2+}\right]\left[OH^{-}\right]^2 > K_{\textit{sp}}}\)

\(\Rightarrow \ce{Mg(OH)2}\) will precipitate.
 

\(\ce{Mg^{2+}(aq) + 2OH-(aq) \rightarrow Mg(OH)2(s)}\)

Since \(K_{\textit{sp}}\) is small, assume reaction goes to completion.

\(\ce{n(Mg^{2+})=0.006\ mol, n(OH^{-})=0.010\ mol}\)

Using stoichiometric ratio \((1:2)\)

\(0.006 > \dfrac{0.010}{2}=0.005\ \ \Rightarrow \ce{Mg^{2+}}\) is in excess.

Concentration drops to: \(6 \times 10^{-3}-5 \times 10^{-3}=1 \times 10^{-3}\).
 

Check if \(\ce{MgCO3}\) will precipitate:

\(\ce{\left[Mg^{2+}\right]\left[CO3^{2-}\right]}\) becomes  \(2 \times 10^{-6} <K_{\textit{sp}}\).

\(\ce{\Rightarrow\ MgCO3}\) won’t precipitate.

Filed Under: Solution Equilibria Tagged With: Band 5, Band 6, smc-3672-10-Mixed ionic solutions, smc-3672-20-Calcs given K(sp), smc-3672-70-Precipitate

PHYSICS, M8 2025 HSC 20 MC

Consider the possibility of an electron and a positron colliding in a particle accelerator to produce a proton and an antiproton, as shown in the equation below.

\(\text{electron}+ \text{positron}\ \rightarrow \ \text{proton}+ \text {antiproton}\)

Which statement makes the correct conclusion about the possibility of such a reaction, and provides a plausible reason for this conclusion?

  1. The reaction is impossible because electrons and positrons will combine to produce a single neutral particle.
  2. The reaction is possible because the masses of the proton and antiproton are the result of their relativistic velocities.
  3. The reaction is possible because the masses of the proton and antiproton come mainly from energy supplied by the accelerator.
  4. The reaction is impossible because protons are much more massive than electrons and hence the reaction violates the law of conservation of mass.
Show Answers Only

\(C\)

Show Worked Solution

Option \(C\) is correct:

  • The electron and positron have very small rest masses compared to protons and antiprotons.
  • The particle accelerator supplies enormous kinetic energy to the electron and positron by accelerating them to speeds close to the speed of light.
  • This kinetic energy can be converted into mass to create the heavier proton-antiproton pair according to Einstein’s \(E = mc^2\) equation.
  • This means conservation of energy is satisfied, even though the products have much greater rest mass than the reactants.
♦ Mean mark 47%.

Other options:

  • The reaction is possible – see above (eliminate \(A\) and \(D\)).
  • Option \(B\) is incorrect. The proton and antiproton’s mass must come from the reactants’ energy (electron + positron + accelerator energy), not from their own relativistic velocities.

Filed Under: Deep Inside the Atom Tagged With: Band 6, smc-3704-25-Linear Accelerator, smc-3704-30-Nuclear Transformation

PHYSICS, M5 2025 HSC 18 MC

The escape velocity from the surface of a planet, which has no atmosphere, is \(v\). A mass is launched at 45° to the planet's surface at \(v\).

What will be the subsequent motion of the mass?

  1. A circular orbit around the planet
  2. An elliptical orbit around the planet
  3. A parabolic trajectory, returning to land with velocity \(v\)
  4. A trajectory reaching zero velocity at an infinite distance
Show Answers Only

\(D\)

Show Worked Solution
  • The mass is launched at escape velocity which means the object has just enough energy to escape the planet’s gravity.
  • As the mass travels away from the planet, kinetic energy converts into gravitational potential energy.
  • Since its initial velocity was exactly escape velocity, at infinite distance, all kinetic energy has been converted to potential energy. This means the velocity reaches zero exactly when the distance becomes infinite.
  • The 45° launch angle does not matter – escape velocity depends only on speed, not direction.

\(\Rightarrow D\)

♦♦♦ Mean mark 29%.

Filed Under: Motion in Gravitational Fields Tagged With: Band 6, smc-3692-70-Escape Velocity

PHYSICS, M5 2025 HSC 36

A satellite with velocity \(v\), is in a geostationary orbit as shown in Figure 1.
 

At point \(Y\), the satellite explodes and splits into two pieces \(m_{ a }\) and \(m_{ b }\), of identical mass. As a result of the explosion, the velocity of one piece, \(m_{ a }\), changes from \(v\) to \(2 v\) as shown in Figure 2.

Analyse the subsequent motion of BOTH \(m_{ a }\) and \(m_{ b }\) after the explosion. Include reference to relevant conservation laws and formulae in your answer.   (8 marks)

--- 22 WORK AREA LINES (style=lined) ---

Show Answers Only

At the point in time of the explosion:

  • By the law of conservation of momentum, the momentum changes of \(m_a\) and \(m_b\) caused by the explosion must be equal in magnitude but opposite in direction.
  • Since their masses are equal, both pieces experience the same change in velocity, but in opposite directions.
  • Because the velocity of \(m_a\) increases by \(v\) in the direction it was already travelling, the velocity of \(m_b\) must also change by \(v\) but in the opposite direction to its original motion.
  • Hence, relative to Earth, the velocity of \(m_b\) becomes zero at that instant.

Motion after the explosion:

  • The satellite’s orbital velocity before the explosion is  \(v_{\text{orb}}=\sqrt{\dfrac{GM}{r}}\)  and the instantaneous velocity of \(m_a\) becomes twice this value.
  • Since  \(2v_{\text{orb}} = 2 \times \sqrt{\dfrac{GM}{r}} >\sqrt{\dfrac{2GM}{r}} \left(v_{\text{esc}}\right)\), the speed of \(m_a\) after the explosion exceeds escape velocity.
  • After the explosion, \(m_a\) continues moving away from Earth with a decreasing speed, but because its initial speed is greater than escape velocity from that point, it will never return. Its total mechanical energy (kinetic + potential) remains constant and positive.
  • Meanwhile, \(m_b\) begins accelerating from an initial velocity of zero toward Earth’s centre. Its initial acceleration is less than \(\text{ 9.8 m s}^{-2}\) because it is not at Earth’s surface. As gravitational force increases, its acceleration also increases, and it continues gaining speed at an increasing rate until it reaches Earth’s atmosphere.
  • In accordance with the conservation of energy, until \(m_b\) reaches the atmosphere, the sum of its kinetic and potential energy remains constant and equal to its initial potential energy immediately after the explosion.
Show Worked Solution

At the point in time of the explosion:

  • By the law of conservation of momentum, the momentum changes of \(m_a\) and \(m_b\) caused by the explosion must be equal in magnitude but opposite in direction.
  • Since their masses are equal, both pieces experience the same change in velocity, but in opposite directions.
  • Because the velocity of \(m_a\) increases by \(v\) in the direction it was already travelling, the velocity of \(m_b\) must also change by \(v\) but in the opposite direction to its original motion.
  • Hence, relative to Earth, the velocity of \(m_b\) becomes zero at that instant.
♦ Mean mark 39%.

Motion after the explosion:

  • The satellite’s orbital velocity before the explosion is  \(v_{\text{orb}}=\sqrt{\dfrac{GM}{r}}\)  and the instantaneous velocity of \(m_a\) becomes twice this value.
  • Since  \(2v_{\text{orb}} = 2 \times \sqrt{\dfrac{GM}{r}} >\sqrt{\dfrac{2GM}{r}} \left(v_{\text{esc}}\right)\), the speed of \(m_a\) after the explosion exceeds escape velocity.
  • After the explosion, \(m_a\) continues moving away from Earth with a decreasing speed, but because its initial speed is greater than escape velocity from that point, it will never return. Its total mechanical energy (kinetic + potential) remains constant and positive.
  • Meanwhile, \(m_b\) begins accelerating from an initial velocity of zero toward Earth’s centre. Its initial acceleration is less than \(\text{ 9.8 m s}^{-2}\) because it is not at Earth’s surface. As gravitational force increases, its acceleration also increases, and it continues gaining speed at an increasing rate until it reaches Earth’s atmosphere.
  • In accordance with the conservation of energy, until \(m_b\) reaches the atmosphere, the sum of its kinetic and potential energy remains constant and equal to its initial potential energy immediately after the explosion.

Filed Under: Motion in Gravitational Fields Tagged With: Band 5, Band 6, smc-3692-40-Satellites

PHYSICS, M8 2025 HSC 33

Analyse the role of experimental evidence and theoretical ideas in developing the Standard Model of matter.   (6 marks)

--- 18 WORK AREA LINES (style=lined) ---

Show Answers Only

Overview Statement

  • The Standard Model’s development depends on the cyclical relationship between experimental evidence and theoretical predictions.
  • These components interact with each other, where theory guides experiments and results validate or refine theory.

Particle Discovery

  • Theoretical predictions lead to targeted experimental searches for specific particles.
  • The Higgs Boson was theoretically proposed decades before its experimental discovery to explain particle mass.
  • Cloud chambers discovered antimatter after theory predicted its existence.
  • Particle accelerators verified quarks existed by revealing the internal structure of protons and neutrons.
  • This pattern shows theory provides the framework while experiments confirm reality.
  • Consequently, successful verification enables confidence in theoretical models and guides further predictions.

Experimental Tools Driving Theoretical Refinement

  • High-energy particle accelerators create small wavelength ‘matter probes’ allowing high-resolution investigation of matter’s structure.
  • These experiments verified electroweak theory by demonstrating electromagnetic and weak nuclear forces result from the same underlying interaction.
  • Unexpected experimental results sometimes cause theoretical modifications or new predictions.
  • The significance is that increasingly powerful experimental tools reveal deeper layers of matter structure.

Implications and Synthesis

  • This reveals the Standard Model emerged from iterative cycles where theory and experiment continuously influence each other.
  • Neither component alone could have produced the model.
  • Together, they form a self-correcting system advancing our understanding of fundamental matter.
Show Worked Solution

Overview Statement

  • The Standard Model’s development depends on the cyclical relationship between experimental evidence and theoretical predictions.
  • These components interact with each other, where theory guides experiments and results validate or refine theory.
♦♦♦ Mean mark 37%.

Particle Discovery

  • Theoretical predictions lead to targeted experimental searches for specific particles.
  • The Higgs Boson was theoretically proposed decades before its experimental discovery to explain particle mass.
  • Cloud chambers discovered antimatter after theory predicted its existence.
  • Particle accelerators verified quarks existed by revealing the internal structure of protons and neutrons.
  • This pattern shows theory provides the framework while experiments confirm reality.
  • Consequently, successful verification enables confidence in theoretical models and guides further predictions.

Experimental Tools Driving Theoretical Refinement

  • High-energy particle accelerators create small wavelength ‘matter probes’ allowing high-resolution investigation of matter’s structure.
  • These experiments verified electroweak theory by demonstrating electromagnetic and weak nuclear forces result from the same underlying interaction.
  • Unexpected experimental results sometimes cause theoretical modifications or new predictions.
  • The significance is that increasingly powerful experimental tools reveal deeper layers of matter structure.

Implications and Synthesis

  • This reveals the Standard Model emerged from iterative cycles where theory and experiment continuously influence each other.
  • Neither component alone could have produced the model.
  • Together, they form a self-correcting system advancing our understanding of fundamental matter.

Filed Under: Deep Inside the Atom Tagged With: Band 5, Band 6, smc-3704-10-Standard Model

PHYSICS, M7 2025 HSC 32

Analyse the consequences of the theory of special relativity in relation to length, time and motion. Support your answer with reference to experimental evidence.   (8 marks)

--- 22 WORK AREA LINES (style=lined) ---

Show Answers Only

Overview Statement

  • Special relativity predicts that time dilation, length contraction and relativistic momentum arise from the principle that the speed of light is constant for all observers.
  • These effects change how time, distance and motion are measured and each consequence is supported by experimental evidence.

Time–Length Relationship in Muon Observations

  • Muon-decay experiments show how time dilation and length contraction depend on relative motion.
  • Muons created high in the atmosphere have such short lifetimes that, in classical physics, they should decay long before reaching Earth’s surface. Yet far more muons are detected at ground level than predicted.
  • In Earth’s frame of reference, the muons experience time dilation, so they “live longer” and travel further.
  • In the muon’s frame of reference, the atmosphere is length-contracted according to the equation  \(l=l_0 \sqrt{\left(1-\dfrac{v^{2}}{c^{2}}\right)}\), so the distance they travel is much shorter.
  • Both viewpoints are valid within their own reference frames, showing that time and length are not absolute but depend on relative motion.

Momentum–Energy Relationship in Particle Accelerators

  • Relativistic momentum explains how objects behave as they approach light speed.
  • Particle accelerators show that enormous increases in energy produce only small increases in speed at high velocities.
  • Particles act as though their mass increases, so each additional acceleration requires disproportionately more energy.
  • This makes it impossible for any object with mass to reach the speed of light, since doing so requires infinite energy.
  • Thus, relativistic momentum preserves light speed as a universal limit.

Implications and Synthesis

  • The consequences of these observations reveal that space and time form a single, interconnected framework rather than separate absolute quantities.
  • At high velocities, motion fundamentally alters measurements of time, distance and momentum.
  • Together, these consequences confirm that classical physics fails at relativistic speeds and that special relativity accurately describes the behaviour of fast-moving objects.
Show Worked Solution

Overview Statement

  • Special relativity predicts that time dilation, length contraction and relativistic momentum arise from the principle that the speed of light is constant for all observers.
  • These effects change how time, distance and motion are measured and each consequence is supported by experimental evidence.
♦ Mean mark 53%.

Time–Length Relationship in Muon Observations

  • Muon-decay experiments show how time dilation and length contraction depend on relative motion.
  • Muons created high in the atmosphere have such short lifetimes that, in classical physics, they should decay long before reaching Earth’s surface. Yet far more muons are detected at ground level than predicted.
  • In Earth’s frame of reference, the muons experience time dilation, so they “live longer” and travel further.
  • In the muon’s frame of reference, the atmosphere is length-contracted according to the equation  \(l=l_0 \sqrt{\left(1-\dfrac{v^{2}}{c^{2}}\right)}\), so the distance they travel is much shorter.
  • Both viewpoints are valid within their own reference frames, showing that time and length are not absolute but depend on relative motion.

Momentum–Energy Relationship in Particle Accelerators

  • Relativistic momentum explains how objects behave as they approach light speed.
  • Particle accelerators show that enormous increases in energy produce only small increases in speed at high velocities.
  • Particles act as though their mass increases, so each additional acceleration requires disproportionately more energy.
  • This makes it impossible for any object with mass to reach the speed of light, since doing so requires infinite energy.
  • Thus, relativistic momentum preserves light speed as a universal limit.

Implications and Synthesis

  • The consequences of these observations reveal that space and time form a single, interconnected framework rather than separate absolute quantities.
  • At high velocities, motion fundamentally alters measurements of time, distance and momentum.
  • Together, these consequences confirm that classical physics fails at relativistic speeds and that special relativity accurately describes the behaviour of fast-moving objects.

Filed Under: Light and Special Relativity Tagged With: Band 4, Band 5, Band 6, smc-3699-10-Time Dilation, smc-3699-20-Length Contraction, smc-3699-30-Momentum Dilation and calcs, smc-3699-50-Scientific Theories

CHEMISTRY, M6 2025 HSC 19 MC

0.1 mol of solid sodium acetate is dissolved in 500 mL of 0.1 mol L\(^{-1}\) \(\ce{HCl}\) in a beaker. This solution has a pH of 4.8 .

500 mL of distilled water is then added to the beaker.

What is the pH of the final solution?

  1. 2.4
  2. 4.5
  3. 4.8
  4. 5.1
Show Answers Only

\(C\)

Show Worked Solution

Strategy 1

  • Sodium acetate + \(\ce{HCl}\) produces a buffer solution (equal moles of weak acid \(\ce{CH3COOH}\) and its conjugate base \(\ce{CH3COO-}\)).
  • A buffer’s pH is independent of dilution (the ratio of [acid]:[conjugate base] stays constant).
  • Therefore pH remains 4.8

Strategy 2 (Quantitative Analysis “trap”)

  • The initial reaction between sodium acetate and hydrochloric acid runs to completion as \(\ce{HCl}\) is a strong acid:
  •    \(\ce{CH3COO-(aq) + HCl(aq) -> CH3COOH(aq) + Cl-(aq)}\)
  • \(n(\ce{CH3COO-}) = 0.1\ \text{mol}\)
  • \(n(\ce{HCl}) = 0.5\ \text{L} \times 0.1\ \text{mol L}^{-1} = 0.05\ \text{mol}\)
  • As they react in a \(1:1\) ratio, \(\ce{HCl}\) is the limiting reagent.
  • \(n(\ce{CH3COO-_{\text{after reaction}}}) = n(\ce{CH3COO_{\text{initial}}})-n(\ce{CH3COO_{\text{reacted}}}) = 0.1-0.05 = 0.05\ \text{mol}\)
  • \(n(\ce{CH3COOH_{\text{after reaction}}}) = n(\ce{CH3COO_{\text{reacted}}}) = 0.05\ \text{mol}\)
  • The following equilibrium reaction is then established below dilution
  •    \(\ce{CH3COOH(aq) + H2O(l) \leftrightharpoons CH3COO-(aq) + H3O+(aq)}\)
  • Therefore the following ice table can be constructed:
♦♦♦ Mean mark 19%.
COMMENT: The key insight here is conceptual not computational.

\begin{array} {|c|c|c|c|}
\hline  & \ce{[CH3COOH]} & \ce{[CH3COO-]} & \ce{[H3O+]} \\
\hline \text{Initial} & 0.1 & 0.1 & 0 \\
\hline \text{Change} & -10^{-4.8} & +10^{-4.8} & +10^{-4.8} \\
\hline \text{Equilibrium} & 0.1-10^{-4.8} & 0.1+10^{-4.8} & +10^{-4.8} \\
\hline \end{array}

\(\therefore K_a = \dfrac{(0.1+10^{-4.8})(10^{-4.8})}{0.1-10^{-4.8}} = 1.585395 \times 10^{-5}\)

  • Then considering the dilution which would shift the equilibrium position to the right.

\begin{array} {|c|c|c|c|}
\hline  & \ce{[CH3COOH]} & \ce{[CH3COO-]} & \ce{[H3O+]} \\
\hline \text{Initial} & 0.1 \times \dfrac{500\ \text{mL}}{1000\ \text{mL}} = 0.05 & 0.1 \times \dfrac{500\ \text{mL}}{1000\ \text{mL}} = 0.05 & 0 \\
\hline \text{Change} & -x & +x & +x \\
\hline \text{Equilibrium} & 0.05-x & 0.05+x & +x \\
\hline \end{array}

  • As \(K_{eq}\) is small, \(0.05 -x \approx 0.05\)  and  \(0.05 + x \approx 0.05\). 
  •    \(\therefore K_{eq} = \dfrac{0.05x}{0.05} = x = 1.585395 \times 10^{-5}\)
  • \(\text{pH} = -\log_{10}\ce{[H3O+]} = -\log_{10}(1.585395 \times 10^{-5}) = 4.79962 = 4.8\ \text{(1 d.p.)}\)

\(\Rightarrow C\)

Filed Under: Bronsted-Lowry Theory, Quantitative Analysis Tagged With: Band 6, smc-3674-15-pH of Mixed Solution, smc-3674-18-Dissociation in Water, smc-3675-30-Ka/Kb, smc-3675-40-Strong/Weak Acids, smc-3675-60-Buffers

CHEMISTRY, M8 2025 HSC 18 MC

The concentration of silver ions in a solution is determined by titrating it with aqueous sodium chloride, using yellow potassium chromate as the indicator.

Which row of the table correctly identifies the colour change at the endpoint and the more soluble salt?

\begin{align*}
\begin{array}{l}
\rule{0pt}{2.5ex} \ & \\
 \ \rule[-1ex]{0pt}{0pt}& \\
\rule{0pt}{2.5ex}\textbf{A.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{B.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{C.}\rule[-1ex]{0pt}{0pt}\\
\rule{0pt}{2.5ex}\textbf{D.}\rule[-1ex]{0pt}{0pt}\\
\end{array}
\begin{array}{|c|c|}
\hline
\rule{0pt}{2.5ex}\ \ \text{Colour change} \ \ & \text{More soluble salt} \\
\text{at endpoint}\rule[-1ex]{0pt}{0pt}& \text{} \\
\hline
\rule{0pt}{2.5ex}\text{Red to yellow}\rule[-1ex]{0pt}{0pt}& \ce{Ag2CrO4}\\
\hline
\rule{0pt}{2.5ex}\text{Yellow to red}\rule[-1ex]{0pt}{0pt}& \ce{Ag2CrO4}\\
\hline
\rule{0pt}{2.5ex}\text{Red to yellow}\rule[-1ex]{0pt}{0pt}& \ce{AgCl} \\
\hline
\rule{0pt}{2.5ex}\text{Yellow to red}\rule[-1ex]{0pt}{0pt}& \ce{AgCl} \\
\hline
\end{array}
\end{align*}

Show Answers Only

\(B\)

Show Worked Solution
  • The two key reactions that take place in this titration are
  •    \(\ce{Ag+(aq) + Cl-(aq) -> AgCl(s)}\)
  •    \(\ce{2Ag+(aq) + CrO4^{2-}(aq) -> Ag2CrO4(s)}\)
  • For the titration to occur effectively all of the \(\ce{Cl-}\) ions must react with \(\ce{Ag+}\) ion and be precipitated out of the solution as the sodium chloride is Titrant (known volume and known concentration).
  • Only once all of the \(\ce{Cl-}\) ions are used up will silver ions begin to react the chromate ions signally the endpoint of the titration.
  • Hence, \(\ce{Ag2CrO4}\) is the more soluble salt and as the potassium chromate is initially yellow, the colour change must be from yellow to red.

\(\Rightarrow B\)

♦♦♦ Mean mark 14%.

Filed Under: Inorganic Substances Tagged With: Band 6, smc-3682-70-Precipitation Titrations

Vectors, EXT2 V1 2025 HSC 16c

Consider the point \(B\) with three-dimensional position vector \(\underset{\sim}{b}\) and the line  \(\ell: \underset{\sim}{a}+\lambda \underset{\sim}{d}\), where \(\underset{\sim}{a}\) and \(\underset{\sim}{d}\) are three-dimensional vectors, \(\abs{\underset{\sim}{d}}=1\) and \(\lambda\) is a parameter.

Let \(f(\lambda)\) be the distance between a point on the line \(\ell\) and the point \(B\).

  1. Find \(\lambda_0\), the value of \(\lambda\) that minimises \(f\), in terms of \(\underset{\sim}{a}, \underset{\sim}{b}\) and \(\underset{\sim}{d}\).   (2 marks)

    --- 12 WORK AREA LINES (style=lined) ---

  2. Let \(P\) be the point with position vector  \(\underset{\sim}{a}+\lambda_0 \underset{\sim}{d}\).
  3. Show that \(PB\) is perpendicular to the direction of the line \(\ell\).   (1 mark)

    --- 7 WORK AREA LINES (style=lined) ---

  4. Hence, or otherwise, find the shortest distance between the line \(\ell\) and the sphere of radius 1 unit, centred at the origin \(O\), in terms of \(\underset{\sim}{d}\) and \(\underset{\sim}{a}\).
  5. You may assume that if \(B\) is the point on the sphere closest to \(\ell\), then \(O B P\) is a straight line.   (3 marks)

    --- 16 WORK AREA LINES (style=lined) ---

Show Answers Only

i.    \(\lambda_0=\underset{\sim}{d}(\underset{\sim}{b}-\underset{\sim}{a})\)

ii.   \(\text{See Worked Solutions.}\)

iii.  \(d_{\min }= \begin{cases}\sqrt{\abs{\underset{\sim}{a}}^2-(\underset{\sim}{a} \cdot \underset{\sim}{d})^2}-1, & \sqrt{\abs{\underset{\sim}{a}}^2-(\underset{\sim}{a} \cdot \underset{\sim}{d})^2}>1 \\ 0, & \sqrt{\abs{\underset{\sim}{a}}^2-(\underset{\sim}{a} \cdot \underset{\sim}{d})^2} \leqslant 1 \ \ \text{(i.e. it touches sphere) }\end{cases}\)

Show Worked Solution

i.    \(\ell=\underset{\sim}{a}+\lambda \underset{\sim}{d}, \quad\abs{\underset{\sim}{d}}=1\)

\(\text{Vector from point \(B\) to a point on \(\ell\)}:\ \underset{\sim}{a}+\lambda \underset{\sim}{d}-\underset{\sim}{b}\)

\(f(\lambda)=\text{distance between \(\ell\) and \(B\)}\)

\(f(\lambda)=\abs{\underset{\sim}{a}-\underset{\sim}{b}+\lambda \underset{\sim}{d}}\)

\(\text{At} \ \ \lambda_0, f(\lambda) \ \ \text{is a min}\ \Rightarrow \ f(\lambda)^2 \ \ \text {is also a min}\)

♦♦ Mean mark (i) 33%.
\(f(\lambda)^2\) \(=\abs{\underset{\sim}{a}-\underset{\sim}{b}+\lambda \underset{\sim}{d}}^2\)
  \(=(\underset{\sim}{a}-\underset{\sim}{b}+\lambda \underset{\sim}{d})(\underset{\sim}{a}-\underset{\sim}{b}+\lambda \underset{\sim}{d})\)
  \(=(\underset{\sim}{a}-\underset{\sim}{b})\cdot (\underset{\sim}{a}-\underset{\sim}{b})+2\lambda (\underset{\sim}{a}-\underset{\sim}{b}) \cdot \underset{\sim}{d}+\lambda^2 \underset{\sim}{d} \cdot  \underset{\sim}{d}\)
  \(=\lambda^2|\underset{\sim}{d}|^2+2 \underset{\sim}{d} \cdot (\underset{\sim}{a}-\underset{\sim}{b}) \lambda +\abs{\underset{\sim}{a}-\underset{\sim}{b}}^2\)
  \(=\lambda^2+2 \underset{\sim}{d} \cdot (\underset{\sim}{a}-\underset{\sim}{b}) \lambda+\abs{\underset{\sim}{a}-\underset{\sim}{b}}^2\)

 

\(f(\lambda)^2 \ \ \text{is a concave up quadratic.}\)

\(f(\lambda)_{\text {min}}^2 \ \ \text{occurs at the vertex.}\)

\(\lambda_0=-\dfrac{b}{2 a}=-\dfrac{2 \underset{\sim}{d} \cdot (\underset{\sim}{a}-\underset{\sim}{b})}{2}=\underset{\sim}{d} \cdot (\underset{\sim}{b}-\underset{\sim}{a})\)
 

ii.    \(P \ \text{has position vector} \ \ \underset{\sim}{a}+\lambda_0 \underset{\sim}{d}\)

\(\text{Show} \ \ \overrightarrow{PB} \perp \ell:\)

♦♦♦ Mean mark (ii) 22%.

\(\overrightarrow{PB}=\underset{\sim}{b}-\underset{\sim}{p}=\underset{\sim}{b}-\underset{\sim}{a}-\lambda_0 \underset{\sim}{d}\)

\(\overrightarrow{P B} \cdot \underset{\sim}{d}\) \(=\left(\underset{\sim}{b}-\underset{\sim}{a}-\lambda_0 \underset{\sim}{d}\right) \cdot \underset{\sim}{d}\)
  \(=(\underset{\sim}{b}-\underset{\sim}{a}) \cdot \underset{\sim}{d}-\lambda_0 \underset{\sim}{d} \cdot \underset{\sim}{d}\)
  \(=\lambda_0-\lambda_0\abs{\underset{\sim}{d}}^2\)
  \(=0\)

 

\(\therefore \overrightarrow{PB}\ \text{is perpendicular to the direction of the line}\ \ell. \)
 

iii.   \(\text{Shortest distance between} \ \ell \ \text{and sphere (radius\(=1\))}\)

\(=\ \text{(shortest distance \(\ell\) to \(O\))}-1\)

♦♦♦ Mean mark (iii) 4%.

\(f\left(\lambda_0\right)=\text{shortest distance \(\ell\) to point \(B\)}\)

\(\text{Set} \ \ \underset{\sim}{b}=0 \ \Rightarrow \ f\left(\lambda_0\right)=\text{shortest distance \(\ell\) to \(0\)}\)

\(\Rightarrow \lambda_0=\underset{\sim}{d} \cdot (\underset{\sim}{b}-\underset{\sim}{a})=-\underset{\sim}{d} \cdot \underset{\sim}{a}\)

\(f\left(\lambda_0\right)\) \(=\abs{\underset{\sim}{a}-\underset{\sim}{b}-(\underset{\sim}{d} \cdot \underset{\sim}{a})\cdot \underset{\sim}{d}}=\abs{\underset{\sim}{a}-(\underset{\sim}{d} \cdot \underset{\sim}{a})\cdot \underset{\sim}{d}}\)
\(f\left(\lambda_0\right)^2\) \(=\abs{\underset{\sim}{a}}^2-2( \underset{\sim}{a}\cdot \underset{\sim}{d})^2+(\underset{\sim}{d} \cdot \underset{\sim}{a})^2\abs{\underset{\sim}{d}}^2\)
  \(=\abs{\underset{\sim}{a}}^2-(\underset{\sim}{a} \cdot \underset{\sim}{d})^2\)
\(f\left(\lambda_0\right)\) \(=\sqrt{\abs{\underset{\sim}{a}}^2-(\underset{\sim}{a} \cdot \underset{\sim}{d})^2}\)

 

\(\text {Shortest distance of \(\ell\) to sphere \(\left(d_{\min }\right)\):}\)

\(d_{\min }= \begin{cases}\sqrt{\abs{\underset{\sim}{a}}^2-(\underset{\sim}{a} \cdot \underset{\sim}{d})^2}-1, & \sqrt{\abs{\underset{\sim}{a}}^2-(\underset{\sim}{a} \cdot \underset{\sim}{d})^2}>1 \\ 0, & \sqrt{\abs{\underset{\sim}{a}}^2-(\underset{\sim}{a} \cdot \underset{\sim}{d})^2} \leqslant 1 \ \ \text{(i.e. it touches sphere) }\end{cases}\)

Filed Under: Equations of Lines and Curves, Vectors and Vector Equations of Lines Tagged With: Band 5, Band 6, smc-1196-40-Perpendicular, smc-1196-48-Spheres, smc-1196-80-3D vectors, smc-7425-35-Perpendicular, smc-7425-50-Circles/Spheres, smc-7425-80-3D vectors

Mechanics, EXT2 M1 2025 HSC 16b

A particle of mass 1 kg is projected from the origin with a speed of 50 ms\(^{-1}\), at an angle of \(\theta\) below the horizontal into a resistive medium.
 

The position of the particle \(t\) seconds after projection is \((x, y)\), and the velocity of the particle at that time is  \(\underset{\sim}{v}=\displaystyle \binom{\dot{x}}{\dot{y}}\).

The resistive force, \(\underset{\sim}{R}\), is proportional to the velocity of the particle, so that  \(\underset{\sim}{R}=-k \underset{\sim}{v}\), where \(k\) is a positive constant.

Taking the acceleration due to gravity to be 10 ms\(^{-2}\), and the upwards vertical direction to be positive, the acceleration of the particle at time \(t\) is given by:

\(\underset{\sim}{a}=\displaystyle \binom{-k \dot{x}}{-k \dot{y}-10}\).    (Do NOT prove this.) 

Derive the Cartesian equation of the motion of the particle, given  \(\sin \theta=\dfrac{3}{5}\).   (5 marks)

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\(y=\left(\dfrac{1-3 k}{4 k}\right) x+\dfrac{10}{k^2} \times \ln \abs{1-\dfrac{k x}{40}}\)

Show Worked Solution

\(\sin \theta=\dfrac{3}{5} \ \Rightarrow \ \cos \theta=\dfrac{4}{5}\)

\(\text{Components of initial velocity:}\)

\(\dot{x}(0)=50\, \cos \theta=50 \times \dfrac{4}{5}=40 \ \text{ms}^{-1}\)

\(\dot{y}(0)=50\, \sin \theta=50 \times \dfrac{3}{5}=-30\ \text{ms}^{-1}\)

♦♦ Mean mark 35%.

\(\text{Horizontal motion:}\)

  \(\dfrac{d \dot{x}}{dt}\) \(=-k \dot{x} \ \ \text{(given)}\)  
\(\dfrac{dt}{d \dot{x}}\) \(=-\dfrac{1}{k \dot{x}}\)  
\(\displaystyle \int dt\) \(=-\dfrac{1}{k} \int \dfrac{1}{\dot{x}}\, d x\)  
\(t\) \(=-\dfrac{1}{k} \ln \dot{x}+c\)  

 
\(\text{When} \ \ t=0, \ \dot{x}=40 \ \Rightarrow \ c=\dfrac{1}{k} \ln 40\)

\(t\) \(=\dfrac{1}{k} \ln 40-\dfrac{1}{k} \ln \abs{\dot{x}}=\dfrac{1}{k} \ln \abs{\dfrac{40}{\dot{x}}}\)
    \(k t\) \(=\ln \abs{\dfrac{40}{\dot{x}}}\)
  \(e^{k t}\) \(=\dfrac{40}{\dot{x}}\)
\(\dot{x}\) \(=40 e^{-k t}\)
\(x\) \(\displaystyle=\int 40 e^{-k t}\, d t=-\dfrac{40}{k} \times e^{-k t}+c\)

 

\(\text{When} \ \ t=0, x=0 \ \Rightarrow \ c=\dfrac{40}{k}\)

   \(x=\dfrac{40}{k}-\dfrac{40}{k} e^{-k t}=\dfrac{40}{k}\left(1-e^{-k t}\right)\ \ldots\ (1)\)
 

\(\text{Vertical Motion }\)

\(\dfrac{d \dot{y}}{dt}\) \(=-k \dot{y}-10 \quad \text{(given)}\)
\(\dfrac{d t}{d \dot{y}}\) \(=-\dfrac{1}{k} \times \dfrac{1}{\dot{y}+\frac{10}{k}}\)
\(t\) \(=-\dfrac{1}{k} \displaystyle \int \dfrac{1}{\dot{y}+\frac{10}{k}} \, d \dot{y}=-\dfrac{1}{k} \ln \abs{\dot{y}+\frac{10}{k}}+c\)

 

\(\text{When} \ \ t=0, \, \dot{y}=-30 \ \ \Rightarrow\ \ c=\dfrac{1}{k} \ln \abs{-30+\frac{10}{k}}\)

\(t\) \(=\dfrac{1}{k} \ln \abs{-30+\frac{10}{k}}-\dfrac{1}{k} \ln \abs{\dot{y}+\frac{10}{k}}\)
  \(=\dfrac{1}{k} \ln \abs{\frac{-30+\frac{10}{k}}{\dot{y}+\frac{10}{k}}}\)
  \(e^{k t}\) \(=\abs{\dfrac{-30+\frac{10}{k}}{y+\frac{10}{k}}}\)
\(\dot{y}\) \(=\left(-30+\dfrac{10}{k}\right) e^{-k t}-\dfrac{10}{k}\)
\(y\) \(=\displaystyle \left(-30+\dfrac{10}{k}\right) \int e^{-kt}\, d t-\int \dfrac{10}{k}\, dt\)
  \(=-\dfrac{1}{k}\left(-30+\dfrac{10}{k}\right) e^{-k t}-\dfrac{10 t}{k}+c\)

 \(\text{When} \ \ t=0, y=0 \ \Rightarrow \  c=\dfrac{1}{k}\left(-30+\dfrac{10}{k}\right)\)

  \(y\) \(=\dfrac{1}{k}\left(-30+\dfrac{10}{k}\right)-\dfrac{1}{k}\left(-30+\dfrac{10}{k}\right) e^{-k t}-\dfrac{10t}{k}\)
  \(=\left(\dfrac{10}{k^2}-\dfrac{30}{k}\right)\left(1-e^{-k t}\right)-\dfrac{10 t}{k}\ \ldots\ (2)\)

 

\(\text {Cartesian equation (using (1) above):}\)

\(x\) \(=\dfrac{40}{k}\left(1-e^{-k t}\right)\)
\(\dfrac{k x}{40}\) \(=1-e^{-k t}\)
\(e^{-k t}\) \(=1-\dfrac{k x}{40}\)
\(-k t\) \(=\ln \abs{1-\dfrac{k x}{40}}\)
\(t\) \(=-\dfrac{1}{k} \ln \abs{1-\dfrac{kx}{40}}\)

 

\(y\) \(=\left(\dfrac{10}{k^2}-\dfrac{30}{k}\right) \times \dfrac{k x}{40}+\dfrac{10}{k^2} \times \ln \abs{1-\dfrac{k x}{40}}\)
  \(=\left(\dfrac{1-3 k}{4 k}\right) x+\dfrac{10}{k^2} \times \ln \abs{1-\dfrac{k x}{40}}\)

Filed Under: Projectiles and Resisted Motion, Resisted Motion Tagged With: Band 5, Band 6, smc-1061-07-Resistive medium, smc-1061-10-R ~ v, smc-7442-92-Vectors, smc-7442-95-Cartesian Path

Proof, EXT2 P1 2025 HSC 16a

Consider the equation

\(z^n \cos\left[n \theta\right]+z^{n-1} \cos \left[(n-1) \theta\right]+z^{n-2} \cos \left[(n-2) \theta\right]+\cdots+z\, \cos\left[\theta\right]=1\)

where  \(z \in \mathbb{C} , \theta \in \mathbb{R} \), and \(n\) is a positive integer.

Using a proof by contradiction and the triangle inequality, or otherwise, prove that all the solutions to the equation lie outside the circle  \(\abs{z}=\dfrac{1}{2}\)  on the complex plane.   (4 marks)

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\(\text{Proof by contradiction}\)

\(\text{Assume}\ \exists\ z \in \mathbb{C},\ \text{where}\ \abs{z} \in\left[0, \dfrac{1}{2}\right],\ \text{and}\)

\(z^n \cos \left[n \theta \right]+z^{n-1} \cos \left[(n-1) \theta \right] + \ldots +z\, \cos \theta=1\)
 

\(\text{Using the triangle inequality}\ \ \left(\abs{x}+\abs{y} \geqslant \abs{x+y}\right):\)

   \(\left|z^n \cos \left[n \theta\right] \right|+\left|z^{n-1} \cos \left[(n-1) \theta\right] \right|+\ldots+|z\, \cos \theta|\)

\(\geqslant\left|z^n \cos \left[n \theta \right] +z^{n-1} \cos \left[(n-1) \theta \right]+\ldots+z\, \cos \theta\right|\)
 

\(1 \leqslant\left|z^n \cos \left[n \theta \right]\right|+\left|z^{n-1} \cos \left[(n-1) \theta \right]\right|+\ldots+|z\, \cos \theta|\)

\(1 \leqslant|z|^n+|z|^{n-1}+\cdots+|z| \quad (\text{since}-1 \leqslant \cos (k \theta) \leqslant 1)\)

\(1 \leqslant (\frac{1}{2})^n+(\frac{1}{2})^{n-1}+\cdots+(\frac{1}{2}) \)

\(1 \leqslant \underbrace{2^{-n}+2^{-n+1}+\cdots+2^{-1}}_{\text{GP:}\  a=2^{-n}, r=2}\)

\(1 \leqslant \dfrac{2^{-n}\left(2^n-1\right)}{2-1}\)

\(1 \leqslant 1-2^{-n}\)

\(2^{-n} \leqslant 0 \ \ \text {(which is not true)}\)

\(\therefore \ \text{By contradiction, the original statement is correct}\)

Show Worked Solution

\(\text{Proof by contradiction}\)

\(\text{Assume}\ \exists\ z \in \mathbb{C},\ \text{where}\ \abs{z} \in\left[0, \dfrac{1}{2}\right],\ \text{and}\)

\(z^n \cos \left[n \theta \right]+z^{n-1} \cos \left[(n-1) \theta \right] + \ldots +z\, \cos \theta=1\)

♦♦♦ Mean mark 10%.

\(\text{Using the triangle inequality}\ \ \left(\abs{x}+\abs{y} \geqslant \abs{x+y}\right):\)

   \(\left|z^n \cos \left[n \theta\right] \right|+\left|z^{n-1} \cos \left[(n-1) \theta\right] \right|+\ldots+|z\, \cos \theta|\)

\(\geqslant\left|z^n \cos \left[n \theta \right] +z^{n-1} \cos \left[(n-1) \theta \right]+\ldots+z\, \cos \theta\right|\)
 

\(1 \leqslant\left|z^n \cos \left[n \theta \right]\right|+\left|z^{n-1} \cos \left[(n-1) \theta \right]\right|+\ldots+|z\, \cos \theta|\)

\(1 \leqslant|z|^n+|z|^{n-1}+\cdots+|z| \quad (\text{since}-1 \leqslant \cos (k \theta) \leqslant 1)\)

\(1 \leqslant (\frac{1}{2})^n+(\frac{1}{2})^{n-1}+\cdots+(\frac{1}{2}) \)

\(1 \leqslant \underbrace{2^{-n}+2^{-n+1}+\cdots+2^{-1}}_{\text{GP:}\  a=2^{-n}, r=2}\)

\(1 \leqslant \dfrac{2^{-n}\left(2^n-1\right)}{2-1}\)

\(1 \leqslant 1-2^{-n}\)

\(2^{-n} \leqslant 0 \ \ \text {(which is not true)}\)

\(\therefore \ \text{By contradiction, the original statement is correct}\)

Filed Under: Converse, Contradiction and Contrapositive Proof, Inequalities, Language and Illustrations of Proofs, Proof and Inequalities Tagged With: Band 6, smc-1207-10-Contradiction, smc-1208-55-Triangle inequality, smc-7422-20-Contradiction, smc-7422-85-X-topic, smc-7423-55-Triangle Inequality

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