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.
Sol.
When two balls are kept on the floor of the train, both of them are moving with the speed of the train. When brakes are applied, the train stopped suddenly but the speed of balls remain the same as there is no force acting on balls. Therefore, these balls seem to move forward in the train.
As the floor is frictionless both the balls will maintain their speed. Therefore, we can say both the balls will be moving at the same speed.