In starting an exercise, a 1.60-m tall person lifts a 2.10 kg book from the the ground so it is 2.20m above the ground. What is the potential energy of the book relative to (a) the ground,and(b) the top of the persons head? (c) What is the work done by the person in part(a)?

Answer 1

(a) From ground, h=2.30m so:
PE=mgh
=1.70kgx9.8m/sx2.30m
= 38.3J

(b)The person is shorter than the distance at which he holds the book from the ground so:
2.30-1.60=0.7m Use the same formula, just substitute 0.7 in for h.

(c)The work in this case is the potential energy of the book relative to ground, so it is equal to answer a.