# A roller-coaster car travels in a complete vertical loop. Explain, using the concept of energy transfer, why the car must be moving faster at the bottom of the loop than at the top of the loop.

> WJEC A-Level Physics (Wales) — 1.5 Circular motion (A-Level only) · Explain · 5 marks

> A roller-coaster car has a mass of 500 kg. It travels in a complete vertical circular loop. The bottom of the loop is at ground level and the top of the loop is 20 m above the ground.

## Mark scheme (5 marks)

1. The car has gravitational potential energy at the top of the loop (because it is raised above the bottom)
2. By conservation of energy, as the car rises, kinetic energy is transferred to gravitational potential energy
3. At the top of the loop the car has less kinetic energy than at the bottom
4. Since kinetic energy is directly proportional to the square of velocity, less kinetic energy means a lower speed
5. Therefore the car moves faster at the bottom than the top because kinetic energy is greatest at the lowest point (where gravitational potential energy is least)

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-roller-coaster-car-travels-in-a-d78fcf5c) · Published by Druglandscape Ltd.