How Do We Calculate Kinetic Friction and Net Force in a Donkey-Cart System?

[CINA]

Homework Statement

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 wheel’s bearings of the cart.
b) The NET force (magnitude and direction) exerted by the surface on the donkey

Homework Equations

Not sure about these:

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

Y) Fn-Fg = 0

I think that's it.

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.

 

[tiny-tim]

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?

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.