A heavy ring of mass m is clamped on the periphery of a light circular disc. A small particle having equal mass is clamped at the centre of the disc. The system is rotated in such a way that the centre moves in a circle of radius r with a uniform speed v. We conclude that an external force
(a) mv2/r must be acting on the central particle
(b) 2mv2/r must be acting on the central particle
(C)2mv2/r must be acting on the system
(d) 2mv2/r must be acting on the ring.
