Physics · May / June 2025 · Paper 12 · Question 13

The diagram shows a cylinder containing air. The piston is free to move inside the cylinder and atmospheric pressure acts outside the cylinder. [diagram: cylinder containing air with a movable piston, thermal energy applied] As the air inside the cylinder is heated, the piston moves to the right. Which quantity decreases?

1. Athe average force exerted on the piston each time that one air particle hits the piston
2. Bthe average speed of the air particles
3. Cthe mass of air inside the cylinder
4. Dthe number of collisions made by air particles with the piston in one second

As printed in the paper