# 2016 hsc engineering multi-choice help (1 Viewer)

#### cloud edwards

##### Member
2016 engineering multi-number 18.
How does one do this (refer to attachment).

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#### Infernal3

##### New Member
Okay - here's what you need to do:

You have to think how much Y (outer one) will spin if pulley X completes a full revolution.

Pulley X's radius is half of Y's (outer one) so if X completes 1 revolution, Y (outer one) will complete 0.5 revolutions (350 is double 175), therefore its speed will be halved - 0.5 * 150 = 75 rpm.

Then if you look at the pulley inside Y, since it is connected to the outer one, it'll have the same speed - 75 rpm.

Looking at Z, its radius is half of Y (inner one), so basically Z will spin twice as fast as Y (the inner one). So its speed will be double - 75 * 2 = 150 rpm.

As for direction, you should be able to visualise it. X is rotating clockwise so Y (both outer and inner ones) will rotate clockwise as well. So Z will also rotate clockwise.

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thanx

#### cloud edwards

##### Member
Thanx man, you're a life saver