A smooth 2-kg collar is attached to a spring having a stiffness of 3 N/m and an unstretched length of 0.75m. If the collar is released from rest at point. A, determine its acceleration and the normal force on the rod at the instant that y= 1m. The force of the spring is found by F=ks, where k is the stiffness and s is the distance the spring is stretched length. please explain.