# A electric motor is used to lift a heavy crate. During this process, 2400 J of electrical energy is supplied to the motor. The motor transfers 1800 J of energy as useful gravitational potential energy to the crate, and the remainder is wasted. Explain what is meant by a useful energy transfer and a waste energy transfer in this context, and state the law that governs the total energy involved in this process.

> Pearson Edexcel International GCSE Physics (4PH1) — 4.1 Energy transfers · Explain · 4 marks

> An electric motor receives 2400 J of electrical energy. It transfers 1800 J of this energy as gravitational potential energy to a crate being lifted. The remaining energy is transferred as thermal energy to the surroundings.

## Mark scheme (4 marks)

1. A useful energy transfer is the transfer of energy that directly serves the purpose of the system — here, the 1800 J transferred to gravitational potential energy in the crate.
2. A waste energy transfer is the transfer of energy to a form that does not directly serve the purpose of the system — here, the 600 J transferred as thermal energy to the surroundings.
3. The waste energy transferred equals 2400 − 1800 = 600 J (thermal energy to surroundings).
4. The law of conservation of energy states that energy cannot be created or destroyed, only transferred, stored or dissipated — so the total energy output (1800 J + 600 J) equals the total energy input (2400 J).

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](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-293777f0) · Published by Druglandscape Ltd.