Question

A student librarian lifts a 2.2 kg book from the floor to a height of 1.25 m. He carries the book 8.0 m to the stacks and places the book on a shelf that is.35 m above the floor. How much work does he do on the book?

Answer 1

Work = Force x distance, where the ONLY distance we care about the distance in the direction of the force.

Suppose there is a 1 kg book on the floor. I pick it up, put it on a table 1 m high, pick it up, place it on the floor, then pick it up again and put it on the table.

Then the net distance I have moved the book against the force of gravity, is 1 m. Hence the total work is

W = mgh
= (1 kg)(9.8 m/s^2)(1 m)