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ENGINEERING, AE 2023 HSC 6 MC

The landing gear on an aircraft uses a hydraulic braking system. A force of 60 N is applied at the master cylinder with a piston diameter of 12 mm.

What is the force at the brake calliper with a piston diameter of 42 mm ?

  1. 4.9 N
  2. 17.14 N
  3. 210 N
  4. 735 N
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\( D \)

Show Worked Solution

→ Pressure is the same in both master cylinder and brake calliper \(\big(P = \frac{F}{A}\big) \)

→ Convert units: \(12\ \text{mm} = \dfrac{12}{1000} = 0.012\ \text{m, 42 mm}\ =\dfrac{42}{1000} =  0.042\ \text{m} \)

→ Using  \(\dfrac{F_2}{A_2} = \dfrac{F_1}{A_1} \):

\(F_2 = \dfrac{F_1 \times A_2}{A_1} = \dfrac{60 \times \ \pi \times 0.021^2}{\pi \times 0.006^2} = 735\ \text{N} \)

\(\Rightarrow D \)

♦ Mean mark 45%.

ENGINEERING, AE 2017 HSC 6 MC

The diagram shows an aerofoil.
 

Which condition needs to be achieved for lift to occur?

  1. Pressure 1<Pressure 2
  2. Pressure 1= Pressure 2
  3. Pressure 1> Pressure 2
  4. Pressure 1+ Pressure 2=0
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`A`

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→ For a net upwards force, the force from pressure below (pushing up) must exceed the force from pressure above (pushing down).

→ Therefore Pressure 1<Pressure 2.

`=A>`

ENGINEERING, AE 2017 HSC 26a

The flaps of an executive jet are controlled using a hydraulic system. A force of 1 kN acts on the 40 mm diameter master piston.
 

What force would need to be developed to move the flap if the slave piston has a diameter of 100 mm?   (3 marks)

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`6.25\ text{kN}`

Show Worked Solution

`P=F/A`

`1000/(pi xx 20^2)` `=F_S/(pi xx 50^2)`  
`F_S` `=(1000 xx pi xx 50^2)/(pi xx 20^2)`  
  `=6250\ text{N}`  
  `=6.25\ text{kN}`  

ENGINEERING, AE 2019 HSC 10 MC

The diagram shows the airflow in a venturi.
 

What does this diagram illustrate?

  1. Coriolis effect
  2. Pascal's principle
  3. Dynamic pressure
  4. Bernoulli's principle
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`D`

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→ Bernoulli’s principle states that the higher the pressure is, the lower the velocity will be.

→ This is illustrated in the diagram as it shows that there is a decreased pressure in the thinner, higher velocity section.

`=>D`


♦ Mean mark 55%.

ENGINEERING, AE 2020 HSC 22d

An air gauge contains air at 750 kPa (gauge) while atmospheric pressure is at 100 kPa. The air at absolute pressure operates a piston of 15 mm diameter.

Calculate the force the compressed air exerts on the piston.  (4 marks)

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`150.45\ text{N}`

Show Worked Solution

`P_(ga)=750\ text{kPa}, \ P_(atm)=100\ text{kPa}, \ D=15\ text{mm}`

`P` `=P_0+rhogh`  
`P_(abs)` `=P_(atm)+P_(ga)`  
  `= 750 + 100`  
  `= 850\ text{kPa}`  

 

`P_(abs)` `=F/A`  
`F` `=P_(abs)xxA`  
`A` `=(piD^2)/4`  
  `=(pixx0.015^2)/4`  
  `=1.77xx10^(-4)\ text{m}^2`  

 

`:.\ F` `=850xx10^3xx1.77xx10^(-4)`  
  `=  150.45\ text{N}`  


♦♦ Mean mark 40%.

ENGINEERING, AE 2021 HSC 9 MC

A pitot tube supplies two pressure readings, total pressure and static pressure.

These pressure readings are then used to determine the

  1. sealed pressure.
  2. dynamic pressure.
  3. standard pressure.
  4. hydrostatic pressure.
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`B`

Show Worked Solution

Dynamic Pressure = Total − Static

`=>B`