# A factory uses an electric motor to lift heavy crates from the ground floor to a storage shelf. The motor is supplied with 6000 J of energy. Only 4200 J of this is usefully transferred to gravitational potential energy in the crates. Explain why the motor cannot transfer all of the supplied energy usefully, and describe TWO ways in which the efficiency of the motor could be improved.

> Edexcel A-Level Physics (9PH0) — 3.1 Charge and current · Explain · 5 marks

> An electric motor in a factory lifts heavy crates onto storage shelves. The motor receives 6000 J of electrical energy from the mains supply. Of this, 4200 J is transferred usefully as gravitational potential energy.

## Mark scheme (5 marks)

1. Energy cannot be created or destroyed (conservation of energy), so the missing energy must be transferred to waste forms rather than lost.
2. Some energy is transferred as heat (and/or sound) due to friction in the motor's moving parts, making it a waste energy transfer.
3. The efficiency of the motor is less than 1 (or 100%) because some of the input energy is wasted.
4. Lubrication of the motor's moving parts reduces friction, so less energy is wasted as heat, increasing efficiency.
5. Thermal insulation around the motor reduces heat transfer to the surroundings, meaning less energy is dissipated as waste, increasing efficiency.

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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-factory-uses-an-electric-motor-6a414dd1) · Published by Druglandscape Ltd.