The collar A slides on the smooth horizontal bar. The spring constant k = 40 lb/ft. The we...

The collar A slides on the 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 the velocity of B when it has moved downward 2 ft from its current position. (See Example 15.8.)