Question

A ball of mass moving with constant velocity $u$ collides with a smoooth horizontal surface at $O$ as show in figure. Neglect gravity and friction. The y-axis is drawn normal to the horizontal surface at the point of impact $O$ and x-axis is horizontal as shown. About which point will the angular momentum of ball be conserved?

• A. Point A
• B. Point B
• C. Point C
• D. None of these

Answer 1

Answer: (B)

Point B

As the ball hits the point O, it will get an impulse towards y direction. Angular momentum is conserved at point about which net torque is zero.

Thus angular momentum of the ball is conserved about point B.