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Work and power – practice for Years 8–9

Sample questions on Work and power with the right answer and a worked solution, from easy to hard. In the Pickles Academy app a child gets new questions of the same kind every time, so they can't just learn the answers by heart.

Subject
Physics
Year
Years 8–9
Curriculum area
Energy

Question types: Work done and power

Rule: Work and power

Work done W = F × s (in joules), power P = W ÷ t (in watts). When lifting, F = m × g.

1 kJ = 1000 J, 1 kW = 1000 W.

Example: 25 kg lifted 2 m in 5 s: F = 250 N, W = 250 × 2 = 500 J, P = 500 ÷ 5 = 100 W

Watch out: Mass is not force: multiply the kilograms by g = 10 N/kg first, then by the distance.

Sample questions

  1. Question 1 Easy

    Children pull a sledge with a force of 50 N for 4 m. How much work do they do?

    Show the solution
    Answer: 200 J

    How it works: W = F × s = 50 N × 4 m = 200 J.

  2. Question 2 Normal

    A crane lifts a 5 kg load 4 m in 10 s. What is its power? Use g = 10 N/kg.

    Show the solution
    Answer: 20 W

    How it works: W = m × g × h = 5 × 10 × 4 = 200 J; P = W ÷ t = 200 J ÷ 10 s = 20 W.

  3. Question 3 Hard

    A 0.5 kW motor runs for 2 minutes. How much work does it do? Give the answer in kJ.

    Show the solution
    Answer: 60 kJ

    How it works: 2 min = 120 s; W = P × t = 0.5 kW × 120 s = 60 kJ.

Related topics

All Physics topics

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