# A electric motor is used to lift boxes onto a warehouse shelf. Explain why the energy transferred to the motor from the electrical supply is always greater than the energy gained by the boxes as gravitational potential energy.

> OCR GCSE Physics A: Gateway Science (J249) — P5.1 Energy stores and transfers · Explain · 4 marks

> An electric motor in a warehouse is connected to the mains supply. It lifts heavy boxes from the floor onto a shelf above. Engineers notice that the motor becomes warm during use.

## Mark scheme (4 marks)

1. Some energy is transferred as a waste energy transfer / not all input energy becomes useful energy
2. Energy is dissipated / transferred to the thermal store of the motor and surroundings (as heat)
3. The useful energy transfer is only the gravitational potential energy gained by the boxes
4. Energy is conserved overall, so total input equals useful output plus waste — efficiency cannot reach 100%

## Key terms

- [gravitational potential energy](https://www.gradenine.co.uk/glossary/gravitational-potential-energy)

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-electric-motor-is-used-to-cb83d44f) · Published by Druglandscape Ltd.