[填空题]
A 330-kg piano slides 3.6 m down a 28° incla7gsg, 5w+j ;m1 nvfuziny unw)* bsnz.(ykjr+:e and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calcula.j k+y(zsw)nr yb*n:ute:
(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