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ENGINEERING, PPT 2017 HSC 21a

Using examples, explain why gears are used in the design of vehicles.   (3 marks)

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→ Speed, rotation direction and torque can all be changed in engineering mechanisms using gears.

→ Different gear ratios with different types of gears can be combined to change direction or increase torque or speed.

→ For example, a truck cannot travel fast but it can carry tonnes of goods, whereas a performance motorcycle is unable to carry any meaningful load but can travel at high speeds.

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→ Speed, rotation direction and torque can all be changed in engineering mechanisms using gears.

→ Different gear ratios with different types of gears can be combined to change direction or increase torque or speed.

→ For example, a truck cannot travel fast but it can carry tonnes of goods, whereas a performance motorcycle is unable to carry any meaningful load but can travel at high speeds.

ENGINEERING, PPT 2019 HSC 13 MC

The diagram shows a seesaw being used by two children, one of mass 25 kg and the other of mass 20 kg. It has a corroded pivot mechanism that reduces its efficiency by 25%.
 

What is the mechanical advantage of the seesaw?

  1. 0.25
  2. 0.75
  3. 0.80
  4. 1.00
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→ If the arms are the same length, then the MA and VR should be 1. 

→ However, the MA is reduced by 25% due to the decrease in efficiency, as losses in efficiency only change the MA, not the VR.


♦ Mean mark 50%.

ENGINEERING, PPT 2022 HSC 21c

To change a tyre on a bus, a system of pulleys, as shown, is used to lift the wheel and tyre to re-fit them back on the bus. The wheel and tyre have a combined mass of 95 kg.
 

What effort is required to lift the wheel and tyre if the efficiency of the pulley system is 80%?   (3 marks)

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Mean mark 56%.