[填空题]
A 1.60-m tall person lifts a 2.10-kg book from the ground so fv(w t2m-2plebelq7. y gf **;gz/srcit is dkszq,y/2r (x2.20 m above the ground. What is the potential energy of the book r,zdy/rxs2q k(elative to
(a) the ground, J
(b) the top of the person’s head? J
(c) How is the work done by the person related to the answers in parts (a) and (b)? J