[填空题]
A 330-kg piano slides 3.6 m down a 2m7mw 6ux7(a lg86 olpc aqcazu 8-n96o0° incline 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. Calculaau nla96co0q 6pc8o-zte:
(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