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Find work done by each of the forces.

  1. Dec 1, 2008 #1
    To start, I have the solution to this problem (with included steps) in front of me. Finding the answer is not the problem.

    What I want to know is, being a beginner in physics, what are the basic thought processes that would cause one to move toward a solution? What does one consider when finding these answers? I hope this question makes sense...

    Here is the problem:


    A grocery cart with a mass of 15 kg is pushed at constant speed along an aisle by a force Fp = 12 N which acts at an angle of 17° below the horizontal. Find the work done by each of the forces on the cart if the aisle is 12 m long.

    work done by the applied force?
    work done by the frictional force?
    work done by the normal force?
    work done by the gravitational force?
     
  2. jcsd
  3. Dec 1, 2008 #2
    anybody?
     
  4. Dec 1, 2008 #3

    robphy

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    First, you must be patient here.

    Start from the definitions.
    Here, what is the definition of "work done by a force"?
    How does this apply to each force?
     
  5. Dec 1, 2008 #4
    I would guess that the work done by a force would mean how much energy is exerted on the object by each one?

    "how does this apply to each force?"
    Well, I know that gravitational and normal oppose eachother, and that applied and frictional oppose eachother.
     
  6. Dec 1, 2008 #5

    robphy

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    Don't guess.
    What definition is given in your textbook? (Or by this forum? [click on "work done" in your own post])
     
  7. Dec 1, 2008 #6
    We don't have a textbook for my class (intro physics), so that makes it a little hard.

    Thanks for pointing me to the link though.


    I see that work is the integral of the dot product of force and displacement, and I have had a lot of calculus (none about physics), so I understand what that means, but I don't know how that relates to my problem with finding four different kinds of work.
     
  8. Dec 1, 2008 #7

    robphy

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    The object undergoes a displacement [tex]\vec d[/tex].
    [To avoid the use of calculus...] Assuming the forces are constant during the displacement,
    the work [tex]W_1[/tex] done by a force [tex]\vec P_1[/tex] is [tex]\vec P_1 \cdot \vec d[/tex], and similarly for each force. If you are not given each force explicitly, you may have to use Newton's Laws or some other information in the problem to determine the forces.
     
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