A uniform rod of length l and mass M rotating about a fixed vertical axis on a smooth horizontal table. It elastically strikes a particle placed at a distance l/3 from its axis and stops. Mass of the particle is

Question

G1 Physics · Accepted Answer

Conserve angular momentum about the fixed axis through the rod's centre during the elastic collision and use kinetic-energy conservation. With impact at ℓ/3 and the rod stopping, the particle mass is 3M/4. Hence B.