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ENGINEERING, PPT 2017 HSC 21c

The diagram shows a gear train.
 

The mechanical advantage of the gear train is 1.6 : 1 with an efficiency of 80%.

Calculate the number of teeth on the driven gear.   (3 marks)

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`18\ text{teeth}`

Show Worked Solution
`n` `=(MA)/(VR)`  
`VR` `=(MA)/n=1.6/0.8=2`  

 

`VR` `=text{Driven}/text{Driver}`  
`:.\ text{Driven}` `=VR xx text{Driver}`  
  `=18\ text{teeth}`  

♦ Mean mark 48%.

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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`296.875\ text{N}`

Show Worked Solution
`W` `= 95 xx 10 = 950\ text{N}`  
`VR` `= 4\text{ (number of ropes to load)}`  
`eta` `= (MA)/(VR)`  
`MA` `= VRxxeta= 4xx0.8= 3.2`  
     
`MA` `= L/E`  
`E` `= L/(MA)= 950/3.2=296.875\ text{N}`  
Mean mark 56%.