A-level · Work, energy & power

Work done by a forceExam-style questions

The work done by a constant force, W = Fd when the force is along the motion and W = Fd cosθ when it acts at an angle, together with work done against gravity and against resistance — and the sign convention that makes a force opposing the motion do negative work.

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19 questions · A Level level · mark scheme and worked solution on each · no sign-up to try

DifficultyAll Level 1 Level 2 Level 3 Level 4 Level 5

1
A small boat of mass $150$ kg is pulled up a straight slipway by a winch. The slipway is inclined to the horizontal at an angle $\alpha$ , where $\tan\alpha = \frac{9}{40}$

The winch cable is attached to the boat and is parallel to a line of greatest slope of the slipway. The winch pulls the boat along this line, at a constant speed, until the boat has moved $8.2$ m up the slipway.

The coefficient of friction between the boat and the slipway is $\frac{1}{4}$

The boat is modelled as a particle and the cable is modelled as being light.

Use the model to find the total work done by the winch in pulling the boat the $8.2$ m up the slipway.

(5 marks)
Level 3 · 5 marksTry it
2
A block is pushed a distance of $6\text{ m}$ along a rough horizontal floor by a constant horizontal force of $25\text{ N}$ . A constant frictional force of $10\text{ N}$ opposes the motion.
(a) Find the work done by the applied force. (1 mark)
(b) Find the work done against friction. (1 mark)
(c) Find the net work done on the block. (2 marks)
Level 3 · 4 marksTry it
3
A sledge is pulled a distance of $15\text{ m}$ along horizontal ground by a rope inclined at angle $\theta$ to the horizontal, where $\cos\theta = 0.6$ . The tension in the rope is $40\text{ N}$ .
(a) Find the work done by the tension. (2 marks)
(b) The motion is opposed by a constant resistance of $12\text{ N}$ . Find the net work done on the sledge. (2 marks)
Level 3 · 4 marksTry it
4
A block of mass $8\text{ kg}$ is pulled at constant speed $10\text{ m}$ up the line of greatest slope of a smooth plane inclined at angle $\theta$ to the horizontal, where $\sin\theta = 0.3$ . Take $g = 10\text{ m s}^{-2}$ .

Find the work done against gravity. (3 marks)
Level 3 · 3 marksTry it
5
A box slides $20\text{ m}$ across a rough horizontal floor. The frictional force on the box is constant at $15\text{ N}$ .
(a) Find the work done against friction. (2 marks)
(b) Explain why the work done BY friction on the box is negative. (1 mark)
Level 3 · 3 marksTry it

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