Read the case given below and answer the questions that follow:
 
A rubber ball and an iron ball of the same size are placed on the smooth floor of a moving train. When the train stops suddenly after brakes are applied, what happens to the balls? In which direction will they move? Will both balls move at the same speed? Explain your answer.
 
, the balls  rolling in the direction in which the train was moving.
 
This is because, after applying the brakes, train  but the balls  due to inertia.
 
Since the mass between two balls is not the same, the inertia of the iron ball is  than the inertia of the rubber ball.
 
Hence, rubber ball rolls  than the iron ball.