Question

Two balls of the same size but of different materials, rubber and iron are kept on the smooth floor of a moving train. The brakes are applied suddenly to stop the train. Will the balls start rolling? If so, in which direction? Will they move at the same speed? Give reasons for your answer.

Answer 1

Yes, the balls will start rolling in the direction in which the train was moving. This is because, after applying the brakes, the train comes to rest but the balls continue to move due to inertia. Since the masses of the balls are different and hence the inertial forces, the balls will move at different speeds. An iron ball that is heavier than the rubber ball will move with a lower speed.