# A comet travels in a highly elliptical orbit around the Sun. Describe and explain how the orbital speed of the comet changes as it moves from its furthest point from the Sun to its closest point to the Sun.

> Pearson Edexcel International GCSE Physics (4PH1) — 8.1 Motion in the universe · Describe and explain · 4 marks

## Mark scheme (4 marks)

1. The orbital speed increases (as the comet moves closer to the Sun)
2. The orbital radius decreases as the comet approaches the Sun
3. From v = 2πr/T, a smaller orbital radius means a greater orbital speed (for a given period) / gravitational force is greater at smaller radius, increasing speed
4. The comet's mass also decreases near the Sun as ice melts and vaporises, which further contributes to its speed being greater

## Key terms

- [orbital speed](https://www.gradenine.co.uk/glossary/orbital-speed)
- [highly elliptical](https://www.gradenine.co.uk/glossary/highly-elliptical)
- [comet](https://www.gradenine.co.uk/glossary/comet)

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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-comet-travels-in-a-highly-e13fd290) · Published by Druglandscape Ltd.