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Determine the work done by the pushing force

  1. Nov 12, 2009 #1

    jacksonpeeble

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


    2. Relevant equations
    P=W/T
    W=F*D

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


    3. 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
     
  2. jcsd
  3. Nov 12, 2009 #2

    Doc Al

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    Hint for a: What's the net force on the cart?
     
  4. Nov 12, 2009 #3

    jacksonpeeble

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

    Thanks for your help in advance!
     
  5. Nov 12, 2009 #4

    Doc Al

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    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?)
     
  6. Nov 12, 2009 #5

    jacksonpeeble

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    I really don't understand... please walk me through this so that I can grasp the concept...
     
  7. Nov 12, 2009 #6

    Doc Al

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    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.
     
  8. Nov 12, 2009 #7

    jacksonpeeble

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    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?
     
  9. Nov 12, 2009 #8

    jacksonpeeble

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