A ball of mass moving with constant velocity `u` collides with a smooth horizontal surface at `O` as shown in Fig. 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?

Options

A. a. Point `A`
B. b. Point `B`
C. c. Point `C`
D. d. none of the above

Answer

B

Explanation

As the normal force exerted by the horizontal surface passes through point `B` the external torque on the ball is zero about point `B`. So the angular momentum of the ball is conserved about point `B` (`:'tau=(dl)/(dt)`)