# A ski racer descends a snow-covered slope. As she moves down the slope, her gravitational potential energy decreases and her speed increases. Explain, in terms of work done and energy transfers, why the ski racer's kinetic energy at the bottom of the slope is less than the loss in her gravitational potential energy.

> Pearson Edexcel International GCSE Physics (4PH1) — 4.2 Work and power · Explain · 4 marks

> A ski racer of mass 65 kg descends a slope. At the top of the slope her speed is negligible. By the time she reaches the bottom, she has descended a vertical height of 40 m but her kinetic energy is only 18 500 J.

## Mark scheme (4 marks)

1. Work is done against friction (or air resistance / resistive forces) as the ski racer moves down the slope
2. This work done against friction transfers energy away from the skier (as a waste/thermal energy transfer to the surroundings)
3. The work done by gravity (equal to the loss in gravitational potential energy) is shared between increasing kinetic energy and doing work against resistive forces
4. By the conservation of energy, the total energy is conserved — the 'missing' energy equals the work done against resistive forces (transferred as thermal energy)

## Key terms

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