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Practice questions · Moments

Force times distance.

Six original Cambridge-style questions on calculating a moment, the principle of moments, balancing a beam, the perpendicular-distance rule, and stating both conditions for equilibrium.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Two rules, two conditions

Moment = F × perpendicular distance.

01
[2 marks]

Define the moment of a force and state its unit.

  • The moment of a force = force × perpendicular distance from the pivot. ✓
  • Unit: newton metre (N m). ✓
02
Calculation
[2 marks]

A force of 20 N acts at a perpendicular distance of 0.30 m from a pivot. Calculate the moment.

moment = F × d = 20 × 0.30

6.0 N m

03
Analysis
[2 marks]

State the principle of moments.

  • For an object in equilibrium, the total clockwise moment about a pivot equals the total anticlockwise moment about the same pivot. ✓✓
04
Calculation
[3 marks]

A uniform beam is pivoted at its centre. A 12 N weight hangs 0.50 m to the left of the pivot. A second weight hangs 0.30 m to the right and the beam balances. Calculate the second weight.

Balance. clockwise = anticlockwise

W × 0.30 = 12 × 0.50 W = 6.0 ÷ 0.30

W = 20 N

05
Analysis
[2 marks]

State the two conditions that must both be satisfied for an object to be in equilibrium.

  • There is no resultant force on it. ✓
  • There is no resultant moment (clockwise moments = anticlockwise moments). ✓
06
Analysis
[2 marks]

When calculating a moment, a student measures the distance along a beam that is tilted, rather than the horizontal distance from the pivot. Explain why this gives the wrong moment.

  • A moment uses the perpendicular distance from the pivot to the line of action of the force. ✓
  • The slanted distance along the beam is longer than the perpendicular distance, so the calculated moment is too large. ✓