Physics - Center of Mass Question with Solution | TestHub
Two friends A and B (each weighing 40 kg) are sitting in a frictionless well having vertical circular smooth wall. They subtend angle 90° at the centre of the well. A rolls a ball of mass 40 kg in the clockwise direction on the platform base towards B along the wall of the well, which B catches. Then similarly B rolls the ball towards A anticlockwise and A catches it. The ball has a fixed speed of 5 m/s. (Neglect catching and throwing time).
When A meets B they catch each other and now they move together i.e. perfectly inelastic collision. What will be the velocity when they (A+B) throw the ball after catching it
Options:
Answer:
Solution:
Throughout the exchange the only external force (wall normal) passes through the centre, so angular momentum about the centre stays zero. When A meets B and they stick (perfectly inelastic), the combined A + B + ball is therefore momentarily at rest. (A+B) of mass 80 kg then throw the 40 kg ball at 5 m/s relative to themselves. Momentum conservation: 40 v = 80 V with v + V = 5, so V = 5/3 m/s. Hence (A+B) recoil at 5/3 m/s. Answer: (B).
