The 4-lb collar is released from rest against the light elastic spring, which has a stif...

The 4-lb collar is released from rest against the light elastic spring, which has a stiffness of 10 lb/in. and has been compressed a distance of 6 in. Determine the acceleration a of the collar as a function of the vertical displacement x of the collar measured in feet from the point of release. Find the velocity v of the collar when x = 0.5 ft. Friction is negligible.