# Determine the work done by the pushing force

Gold Member

## Homework Statement

A person pushes a 16.0-kg shopping cart at a constant velocity for a distance of 28.0 m. She pushes in a direction 24.0° below the horizontal. A 32.0-N frictional force opposes the motion of the cart.
a. What is the magnitude of the force that the shopper exerts?
b. Determine the work done by the pushing force.
c. Determine the work done by the frictional force.
d. Determine the work done by the gravitational force.

## Homework Equations

P=W/T
W=F*D

I'm sure I'll have to take the cosine of 24 in there somewhere...

## The Attempt at a Solution

a. I assumed this would just be 16*28*cos(24), but this doesn't work. Once I have this, I can solve for B and probably C.
b.
c.
d. w=0

## Answers and Replies

Doc Al
Mentor
Hint for a: What's the net force on the cart?

Gold Member
Net force is equal to mass times acceleration. I have no acceleration, and the answer is not zero...?

Thanks for your help in advance!

Doc Al
Mentor
Net force is equal to mass times acceleration. I have no acceleration, and the answer is not zero...?
The answer to my question is certainly zero. The net force on the cart is zero. Now examine the horizontal force components acting on the cart. Use the fact that they must add to zero to write an equation for the applied force. (If the applied force is F, what is its horizontal component?)

Gold Member
I really don't understand... please walk me through this so that I can grasp the concept...

Doc Al
Mentor
Start by identifying all the forces acting on the cart and which way they act. You should draw a diagram showing those forces. Then consider the horizontal components.

Gold Member
Thank you very much for your help! From it, I was able to find a (35.028) and b (896.001). However, oddly, I still cannot figure out c. Any suggestions?

Gold Member
Nevermind :-) I forgot work could be negative...