A smooth semicircular wire track of radius R is fixed in a vertical plane (see Fig.6.201). One end of a massless spring of natural length (3/4) R is attached to the lowest point o of the wire track. A small ring of mass m, which can slide on the track, A small ring of mass m, which can slide on the track, is attached to the other end of the spring. The ring is held stationary of point P such that the spring makes an angle of 60 0 with the vertical. The spring constant k=(mg/R). Consider the instant when the ring is making an angle 60 degree with the vertical.