A smooth semicircular wire track of radius R is fixed in a vertical plane. One end of massless spring of natural length$3\text{R/4}$ 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 $\text{60°}$ with the vertical. The spring constant is$\text{K}=\text{mg/R}$ . Considering the instance when the ring is released, the free body diagram of the ring, when ${\text{a}}_{\text{r}}$ is tangential acceleration, F is restoring force and N is normal reaction is: