A disc of mass 0.2 kg is kept floating in air without falling by vertically firing bullets each of mass 0.05 kg on the disc at the rate of 10 bullets per every second. If the bullets rebound with the same speed, then the speed of each bullet is

(Acceleration due to gravity $=10 \mathrm{~ms}^{-2}$ )

A body moving along a straight line collides another body of same mass moving in the same direction with half of the velocity of the first body. If the coefficient of restitution between the two bodies is 0.5 , then the ratio of the velocities of the two bodies after collision is (Treat the collision as one dimensional)

The co-ordinates of the centre of mass of a uniform $L$ shaped plate of mass 3 kg shown in the figure is

Three blocks $A, B$ and $C$ are arranged as shown in the figure such that the distance between two successive blocks is 10 m . Block $A$ is displaced towards block $B$ by 2 m and block $C$ is displaced towards block $B$ by 3 m . The distance through which the block $B$ should be moved, so that the centre of mass of the system does not change is