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Moments, levers and gears: GCSE Combined Science Physics practice questions

Foundation and Higher · Grade 6

A second set of questions on moments, levers and gears. They are different from the ones on the topic page. Try each, then open the answer and compare your working.

More questions

Question 1 Hard

A 50 N effort pushes down 0.8 m from the pivot of a lever. The load is 0.1 m from the pivot. What is the largest load the lever can just balance?

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Answer: 400 N

  1. Effort moment = 50 × 0.8 = 40 N m.
  2. Load × 0.1 = 40, so load = 400 N.

Question 2 Hard

A gear with 12 teeth turns at 90 revolutions per minute and drives a gear with 36 teeth. Work out the speed of the larger gear.

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Answer: 30 revolutions per minute

  1. The larger gear has 3 times as many teeth.
  2. 90 ÷ 3 = 30 revolutions per minute.

Question 3 Hard

A 4 m plank is pivoted at its centre. A child weighing 200 N sits 1.5 m from the pivot. Where must a child weighing 300 N sit on the other side to balance it?

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Answer: 1.0 m from the pivot

  1. 200 × 1.5 = 300 N m.
  2. 300 × d = 300, so d = 1.0 m.

Question 4 Hard

In the gear question where 12 teeth drives 36 teeth, how does the moment on the larger gear compare with the moment on the smaller gear?

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Answer: three times bigger

  1. The larger gear turns three times slower.
  2. Ignoring losses its moment is three times bigger.

Quick checks

Short questions with options. Choose one before you open the answer.

Check 1

What is a pivot?

  1. the fixed point an object turns about
  2. the heaviest part of a lever
  3. the force you push with
Show answer

the fixed point an object turns about A pivot is the point an object rotates around, such as the hinge of a door.

Check 2

What is the moment of a force?

  1. how fast the object moves in a line
  2. its turning effect about a pivot
  3. the weight of the object
Show answer

its turning effect about a pivot A moment is how strongly a force makes an object turn about a pivot.

Check 3

What is the equation for a moment?

  1. moment = force ÷ distance
  2. moment = force + distance
  3. moment = force × perpendicular distance from the pivot
Show answer

moment = force × perpendicular distance from the pivot A moment is force multiplied by the perpendicular distance from the pivot.

Check 4

What is the unit of a moment?

  1. the newton metre, N m
  2. the newton, N
  3. the watt, W
Show answer

the newton metre, N m Force is in newtons and distance is in metres, so a moment is in newton metres.

Check 5

What does perpendicular distance mean?

  1. the distance along the line of the force
  2. the distance at right angles to the line of the force
  3. the distance from the pivot to the edge of the object
Show answer

the distance at right angles to the line of the force Measure from the pivot to the force line, at 90 degrees to it.

Check 6

What does anticlockwise mean?

  1. turning the opposite way to the hands of a clock
  2. turning the same way as the hands of a clock
  3. moving in a straight line
Show answer

turning the opposite way to the hands of a clock Anticlockwise is the opposite direction to the hands of a clock.

Check 7

What is the principle of moments?

  1. The forces up always equal the forces down.
  2. For a balanced object, total clockwise moment = total anticlockwise moment.
  3. The heavier side sits further from the pivot.
Show answer

For a balanced object, total clockwise moment = total anticlockwise moment. A balanced object is not turning, so the two kinds of moment cancel.

Check 8

A force of 10 N acts 0.3 m from a pivot. What is the moment?

  1. 33 N m
  2. 10.3 N m
  3. 3 N m
Show answer

3 N m moment = 10 × 0.3 = 3 N m.

Check 9

A force of 30 N acts 20 cm from a pivot. What is the moment in N m?

  1. 6 N m
  2. 600 N m
  3. 1.5 N m
Show answer

6 N m Change 20 cm to 0.2 m, then 30 × 0.2 = 6 N m.

Check 10

A force of 4 N makes a moment of 12 N m. How far from the pivot does it act?

  1. 48 m
  2. 3 m
  3. 8 m
Show answer

3 m distance = moment ÷ force = 12 ÷ 4 = 3 m.

Check 11

Why is a door easier to push at the handle than near the hinge?

  1. The force is further from the pivot, so the moment is bigger.
  2. The handle makes the door lighter.
  3. You automatically push harder at the handle.
Show answer

The force is further from the pivot, so the moment is bigger. Same force, bigger distance, bigger moment.

Check 12

A see-saw balances. A heavy child sits near the pivot. Where is a light child?

  1. nearer to the pivot than the heavy child
  2. further from the pivot
  3. the same distance from the pivot
Show answer

further from the pivot The smaller force needs the bigger distance so the moments are equal.

Check 13

A student works out 10 N × 0.5 m = 5 N. What is wrong?

  1. The answer should be 20 N.
  2. The distance should have been added.
  3. The unit should be N m, not N.
Show answer

The unit should be N m, not N. A moment is measured in newton metres.

Check 14

What is a lever?

  1. a rod that turns about a pivot to move a load
  2. a type of gear
  3. a spring that stores energy
Show answer

a rod that turns about a pivot to move a load A lever turns about a pivot so an effort can move a load.

Check 15

What is the effort of a lever?

  1. the weight being lifted
  2. the force you apply to it
  3. the pivot
Show answer

the force you apply to it The effort is the force you push or pull with.

Check 16

What is the load of a lever?

  1. the force or weight the lever has to move
  2. the force you apply
  3. the fixed point it turns about
Show answer

the force or weight the lever has to move The load is the thing the lever is moving or lifting.

Check 17

How does a long lever help you lift a heavy load?

  1. A small effort far from the pivot can balance a large load near it.
  2. It makes the load weigh less.
  3. It makes the effort move a shorter distance.
Show answer

A small effort far from the pivot can balance a large load near it. Equal moments mean a small force at a large distance balances a large force at a small distance.

Check 18

A lever has a 20 N effort 0.6 m from the pivot. The load is 0.2 m from the pivot. What load can it balance?

  1. 6.7 N
  2. 20 N
  3. 60 N
Show answer

60 N effort moment = 20 × 0.6 = 12 N m, so load × 0.2 = 12 and load = 60 N.

Check 19

What are gears?

  1. toothed wheels that mesh together to pass on a turning effect
  2. springs that store energy
  3. levers that never turn
Show answer

toothed wheels that mesh together to pass on a turning effect Meshing teeth carry the turning effect from one wheel to the next.

Check 20

Gear A turns anticlockwise and meshes with gear B. Which way does B turn?

  1. anticlockwise
  2. clockwise
  3. It does not turn.
Show answer

clockwise Meshing gears turn in opposite directions.

Check 21

A small gear drives a large gear. What happens to the speed and the moment?

  1. The speed is lower and the moment is bigger.
  2. The speed is higher and the moment is bigger.
  3. The speed is lower and the moment is smaller.
Show answer

The speed is lower and the moment is bigger. The larger gear turns slower and has a bigger turning effect.

Check 22

A 10-tooth gear turns at 60 rpm and drives a 20-tooth gear. What is the speed of the larger gear?

  1. 120 rpm
  2. 60 rpm
  3. 30 rpm
Show answer

30 rpm The larger gear has twice the teeth, so it turns at half the speed.

Check 23

Why do you use a low gear on a bike going uphill?

  1. The larger back gear turns the wheel more slowly with a bigger turning effect.
  2. It makes the bike weigh less.
  3. It lets you pedal faster for the same speed.
Show answer

The larger back gear turns the wheel more slowly with a bigger turning effect. A bigger turning effect at the wheel helps you climb.

Check 24

A rider says gears give you extra energy. What is wrong?

  1. Gears waste all of the energy.
  2. Gears change speed and turning effect. They do not create energy.
  3. Gears make the pedals heavier.
Show answer

Gears change speed and turning effect. They do not create energy. Some energy is even wasted as heat by friction.

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