A particle of mass ‘m’ moves on the axis of a ring of radius ‘R’ and mass M. If particle at rest is released from ‘P’  then its kinetic energy at centre c will be

distance of the mass m from the ring is (3R)2+R2 =2R initial potential energy = -GMm2R and final potential energy when at the center is -GMmRkinetic energy is the difference in potential energy