A particle of mass m is projected towards a wall such that theangle of incidence is `theta` and the speed just before collision is u. Assumming that the wall is smooth and the collision is elastic,show that the ball rebonunds at same angle.

Explanation

The situation shown in figure. As the collision is elastic,thereis no loss of energy and hence speed of rebound is same.

The contact forrce between thewall and ball is along the normal, as friction is absent. So the magnitude ofmomentum of ball along the wall must not change
Now,v=u (No loss of energy)
Also `v sinphi=usintheta`(Noforce along the wall)
`theta=phi`