The collar A slides on a smooth horizontal bar. the spring constant k = 40 lb/ft. the weights are Wa = 30 lb and Wb = 60 lb.

The collar A slides on a smooth horizontal bar. the spring constant k = 40 lb/ft. the weights are Wa = 30 lb and Wb = 60 lb. At the instant shown, the spring is unstretched and B is moving downward at 4 ft/s. Use conservation of energy to determine velocity of B when it has moved downward 2 ft from its current position.