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 ball start rolling ?

Answer 1

I think it's rubber ball

Answer 2

$\colorbox{orchid}{ANSWER!}$

Yes, both will start rolling due to inertia of motion. As the masses of the two balls are different, the inertial forces on them will be different and therefore, they will move witg different speeds. The balls will move in the direction in which the train was moving.