A librarian picks up a 22N book from the floor to a height of 1.25m, then carries the book 8m to the stacks and places the book on a shelf that is .35m above the floor. Determine how much total work on the book he does from beginning to end.

Question

anonymous · Answer

I got 35.2J...but the answer is supposed to be 7.7J?

egenriether · Answer

Recall that the work done by the librarian is positive when he lifts the book against gravity and negative when he lowers it in the gravitational field (when the force and displacement are in the same direction the work is positive.)  In this problem it's best to remember what displacement actually takes place: he only ends up lifting the book 0.35m off the ground.  All of the work/energy he put into the book in the initial lift was given back to him when he lowered the book.  So 0.35m*22N=7.7J

anonymous · Answer

oh okay I get it, I forgot d was for displacement and not distance