[填空题]
A 1.60-m tall person lifvc(-k/q- w+kkiii v7 cts a 2.10-kg b ; lpy4x2:r;j svbfg*jook from the ground so it is 2.20 m above the ground. What isbvx* l;sygp; j: j4rf2 the potential energy of the book relative 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