[填空题]
A 330-kg piano slides 3.6 m down a 28° incline a.hsx k 1zf/wmc+ylty 461 29ofbutdh ;nd is kept fromnlj*lwdy/2h67s qji( accelerating by a man who is pushing back on it parallel to the inclisnl ih /j27w(djlqy*6 ne (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man, N
$(b)$ the work done by the man on the piano, J
$(c)$ the work done by the friction force, J
$(d)$ the work done by the force of gravity, J
$(e)$ the net work done on the piano J
