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Homework Help: Finding kineitic friction

  1. Oct 15, 2008 #1
    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 wheel’s bearings of the cart.
    b) The NET force (magnitude and direction) exerted by the surface on the donkey

    2. Relevant equations
    Not sure about these:

    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. jcsd
  3. Oct 16, 2008 #2


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    Science Advisor
    Homework Helper

    Hi CINA! :smile:

    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. :smile:
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