Q. A smooth semi-circular wire-track of radius R is fixed in the vertical plane. One end Of a massless spring of natural length 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 spring, The spring constant K =mg/R. At the instant 
when the tings is released, determine the tangential acceleration of the ring.