# Homework Help: Lifting Books - Potential Energy

1. Jun 20, 2011

### Ipos Manger

1. The problem statement, all variables and given/known data
A student has six books, all of them with a 4cm thickness and a weight of 30N. ¿What would be the minimum work to put the books in one pile, if the six books are in a table?

Weight: 30N
Thickness: 4cm.
Gravity: 9.81ms-2

2. Relevant equations

Ep=mgh

Ec=(mv2)/2

3. The attempt at a solution

I found the mass of each book, which is 3.06kg, and converted the thickness to m, 0.04m.

After that, i'm lost. :S I don't know how to work it out..

2. Jun 20, 2011

### Encephalon

You need to find the amount of work it takes to put one book on top of another book! You know that the work needed to move one book onto the other one is:

(the mass of the book) * (the acceleration due to gravity) * (the height the book must be lifted).

Think about what the height will be that you must lift each book (HINT: it's a number that will increase for each book you stack onto your stack!)

3. Jun 20, 2011

### PhanthomJay

Your relevant equations talk about potential and kinetic energy, but I think you are looking for the minimum work done by the student (not the total work done, although the problem is not worded clearly that way). Minimum work ocurs when the books are moved slowly at constant speed. What equations do you know for work done at constant speed?