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 with the same speed? Give reasons for your answer.

Answer 1

1. The balls would start rolling due to their inertia of motion. As the train was moving, the balls kept on the floor were also in motion with the train. But on the application of a sudden brake, the train stopped but the balls move forward due to their inertia. This is because the inertia of motion tries to keep the body in a uniform motion in a straight line.
2. The balls move in the direction in which the train was moving. This is because their previous motion was in the direction of the train’s motion. And due to the virtue of inertia, they try to keep to their initial motion. Hence, they move forward on the train.
3. The balls will not move with the same speed. The rubber ball will have a greater speed than the iron ball. It will move faster. Mass is the measure of inertia. Objects with greater mass possess greater inertia. The inertia of an iron ball is greater than a rubber ball due to mass. Hence, the rubber ball will move faster.
4. Yes, the balls would start rolling. The balls would start rolling in the direction in which the train was moving. The balls will not have the same speed. A rubber ball will move faster than the iron ball.