The 50-lb block rests on the rough surface for which the coefficient of kinetic friction i...

The 50-lb block rests on the rough surface for which the coefficient of kinetic friction is μk = 0.2. A force F = (40 + s2) lb, where s is in ft, acts on the block in the direction shown. If the spring is originally unstretched (s = 0) and the block is at rest, determine the power developed by the force the instant the block has moved s = 1.5 ft.