A ball kept in a close box moves in the box making collisions with the walls. The box is kept on a smooth surface. The velocity of the centre of mass

Options

A. of the box remains constant
B. of the box plus the ball system remains constant
C. of the ball remains constant
D. of the ball relative to the box remains constant

Answer

B

Explanation

At the time of collision impulsive force are internal for box plus ball system.