Physics · OCR H556 · Topic 3.3

Work, energy and power

Work and conservation of energy, kinetic and potential energies, power.

3 sub-topics
Taught in Year 12
44 practice questions
3 animated lessons

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What the specification says

Every sub-topic OCR can examine in this topic, with its reference number from the official specification. The Y12 and Y13 tags show when each sub-topic is usually taught.

3.3.1Work and conservation of energyY12
3.3.2Kinetic and potential energiesY12
3.3.3PowerY12

Try 2 questions

Easy and medium questions from this topic, each with a worked solutions and the mark for every step. All 44 questions in this topic, free, no account needed.

Mechanics

Easy

Power · Year 12 · 1 mark

A car travels at a constant 15 m s⁻¹ against a total resistive force of 900 N. What is the useful output power of the engine?
(1)

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At constant speed the driving force equals the resistive force, and $P = Fv$ .A: $13.5\ \mathrm{kW}$

Total1

MMethod mark: for a correct method, even with a slip.
AAccuracy mark: for a correct answer from a correct method.
BIndependent mark: for a correct fact or result on its own, with no method needed.

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Mechanics

Medium

Work done · Year 12 · 5 marks

A box is dragged 15 m along level ground by a force of 80 N acting at 40° above the horizontal.

(a)
Define work done.
(1)
(b)
Calculate the work done by the force.
(2)
(c)
The box moves at constant speed. State the work done against friction, explaining your answer.
(2)

Check your answer before you look at the solution

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Part (a)1 mark

Force × distance moved in the direction of the force.

Part (b)2 marks

$W$ ${}= Fd\cos\theta$ ${}= 80 \times 15 \times \cos 40^\circ$
$W = 919\ \mathrm{J}$

Part (c)2 marks

$W_f = 919\ \mathrm{J}$
No kinetic energy is gained, so all the work done goes against friction.

Total5

MMethod mark: for a correct method, even with a slip.
AAccuracy mark: for a correct answer from a correct method.
BIndependent mark: for a correct fact or result on its own, with no method needed.