A smooth semicircular wire track of radius R is fixed in a vertical plane. One end of massless spring of natural length $\frac{3R}{4}$  is attached to the lowest point O of the wire 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 at point P such that the spring makes an angle of 60º with the vertical. The spring constant is $\mathrm{K}=\frac{mg}{R}$.Considering the instance when the ring is released , the free body diagram of the ring, when a_T is tangential acceleration, F is restoring force and N is normal reaction is