# Explain why, when a hot metal spoon is placed into a cup of cold water and the system is left for a long time, the final temperature of the spoon and the water is the same.

> IB DP Physics Standard Level (2023 syllabus) — B.1 Thermal energy transfers · Explain · 4 marks

> A metal spoon at 80 °C is placed into a cup of water at 20 °C. The cup is thermally insulated from its surroundings.

## Mark scheme (4 marks)

1. The particles of the hot spoon have greater average kinetic energy than the particles of the cold water.
2. Thermal energy is transferred from the spoon to the water (by conduction through collisions between particles at the interface).
3. The spoon loses internal energy (cools) and the water gains internal energy (warms) until their average particle kinetic energies are equal.
4. At thermal equilibrium, there is no net transfer of energy between the spoon and the water, so the temperature remains constant and equal for both.

## Related

- [Revision notes for IB DP Physics Standard Level (2023 syllabus)](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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