Question

A 485-g book is resting on a desk 62 cm high. Calculate the book's gravitational potential energy relative to the desktop.

Answer 1

Why is it 0.0 J?

Answer 2

whats the formula for potential energy?

Answer 3

Pg = mass * gravity * height

= .485 * 9.8 * .62 = 2.94686 kg (m/s)^2

http://www.wolframalpha.com/input/?i=2.94686+kg+m%5E2%2Fs%5E2

which should be the same in joules

Answer 4

Eg = mgh

Answer 5

but why is it, 0.0 J?

Answer 6

relative to the desktop

Answer 7

its 0 meters from teh desktop

Answer 8

relative to the ground; its got 2.9 J

relative to the desktop; its got 0 j

Answer 9

ohh, i get it now. Thanks!

Answer 10

Hi there,

All depends of the refrence point, check this: