Joshi sir comment

In a gravity free space a small ball is placed at the centre of a box of the same mass. The ball and the box both are moving with velocity u towards a fixed wall. Assume all collisions are perfectly elastic.

A) How many collisions are possible?

B) find velocities of the box and the ball and the position of the ball relative to the box after all possible collisions.

pls solve question 8

. Dear Sir kindly help solve this question

A point source of light is placed at the centre of curvature

of a hemispherical surface. The radius of curvature is r

and the inner surface is completely reflecting. Find the

force on the hemisphere due to the light falling on it if

the source emits a power W.