There are 2 situations-
1)a rod of length L is lying on a smooth horizontal surface with its one end hinged to the ground, a ball travelling with a velocity v hits its other end and comes to rest, How is the net external torque about hinge point O zero?
2) in the second case, the same rod is lying on the same surface but it is not hinged and is free to move, the same ball hits it again- how is the net torque about center of rod zero?
3. The Attempt at a Solution
I understand that in the first case torque of hinge force about hinge is zero, but when the ball hits the rod it'll impart a non zero torque about O- how is the angular momentum conserved about O then?
In the second case, the ball should again provide a torque about COM, also why isn't torque about any other point also zero since the rod isn't hinged in the second case