# Homework Help: Finding kineitic friction

1. Oct 15, 2008

### CINA

1. The problem statement, all variables and given/known data
A 255[kg] donkey is pulling on a cart with a horizontal force of 1940[N]. The mass of the cart is 520[kg] and the cart is rolling at a constant velocity of 0.72[m/s] to the left.

Find: a) The coefficient of kinetic friction for the wheelâ€™s bearings of the cart.
b) The NET force (magnitude and direction) exerted by the surface on the donkey

2. Relevant equations

X) -Fc/d + Ff = 0 <-- Friction has to be in the direction of the motion since thats what causes it to move, right?

Y) Fn-Fg = 0

I think thats it.

3. The attempt at a solution

I don't really know where to be begin. Is 1940 N the force on the whole system, donkey plus cart? Do I need a FBD for donkey and cart or just one with both? I'm lost, please help.

2. Oct 16, 2008

### tiny-tim

Hi CINA!

1940 N is the force on the cart only.

For a) you need an FBD for the cart, for b) you need an FBD for the donkey.