Quick questions on Energy: work, power, efficiency and conservation - WJEC A-Level Physics

3short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is work?

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When the force is perpendicular to the motion (

\theta = 90^\circ

), no work is done. This is why the tension in a string holding a conical pendulum, or the magnetic force on a moving charge, does no work even though a force clearly acts.

What is q1?

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1500\,\text{W}

motor lifts a

30\,\text{kg}

load. Find the time to raise it

4.0\,\text{m}

, assuming 100 per cent efficiency. Take

g = 9.81\,\text{m s}^{-2}

What is q2?

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Define the efficiency of a device. [1 mark]

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