An 8.0-kg history textbook is placed on a 1.25-m high desk. How large is the gravitational potential energy of the textbook-earth system relative to the desktop?

6 answers

relative to the floor it is m g h but relative to the desktop it is zero. You can do no work moving it down to the desk top if it is already on the desk top.
98 J
8.0 x 9.8 x 1.25
Wah ha ha ha ha ha
98 j
gravitational potential energy (J) = mass(kg) . gravity (N/kg) . height (m),
GPE = mgh 98J
980 J