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Unit summary

Revise!

1. Why is the work done by simple machines always 5. The length of the shorter arm of a lever is 5 cm
greater than useful work? and the length of the longer arm is 30 cm. A
12 N force acts on the shorter arm. What force
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2. Break a match into two equal parts, then break
each piece in half again, and keep breaking it into should be applied to the longer arm to balance
smaller pieces. Why are small pieces more difficult the lever? Draw a picture to illustrate your answer.
to break than larger ones? (The mass of the lever can be disregarded.)
6. 2 N and 18 N forces act on a lever’s ends. The
3. Why does a crane have a counterweight?
length of the lever is 1 m. Where should the pivot
be if the lever is in equilibrium? (The mass of the
lever can be disregarded.)
counterweight
7. What type of simple machine is each object a–d?

A B
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4. A girl drew a diagram of a lever in equilibrium. C D
Find the mistake she made in the image below.

A O B

6 H 6 H

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