# How much work is done on the box by person pulling?

1. Oct 22, 2008

### Bones

1. The problem statement, all variables and given/known data

In the figure below,

http://www.webassign.net/userimages/jshemwell@lincolnpark.il/Net Force/Pulling_at_angle.gif

the mass is 4.00 kg, and = 30 degrees. The surface does have friction, with s = .45 and k = .39.

If a person takes hold of the rope and, pulling at this angle with a force of T = 29 N, drags the box 3.3 meters...

a. How much work is done on the box by person pulling?

b. How much work is done on the box by the normal force?

c. How much work is done on the box by the force of friction?

d. What is the net work done on the box?

e. If the block starts from rest, what will be its velocity just as the person finishes pulling?

2. Relevant equations

3. The attempt at a solution

a) 29N*3.3m*cos30 = 82.9 J
b) 0
c) I took 4kg*9.8m/s^2*0.39*3.3m*cos180 = -50.45 which is not correct. What am I doing wrong??

Last edited: Oct 22, 2008
2. Oct 22, 2008

### Bones

I can figure out the rest, I just need to know what I am doing wrong in part c. I am stuck on part c.

3. Oct 22, 2008

### LowlyPion

The force of friction over the distance.

W = F * d = u*(m*g - T*sinθ ) * d

4. Oct 23, 2008

### Bones

Thanks again!