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Homework Help: Coefficient of Kinetic Friction for crate

  1. Sep 11, 2007 #1
    1. The problem statement, all variables and given/known data

    A 1500 N crate is being pushed across a level floor at a constant speed by a force F of 700 N at an angle of 20° below the horizontal.

    What is the coefficient of kinetic friction between the crate and the floor?

    2. Relevant equations

    3. The attempt at a solution

    I tried 700cos20/1500 + 1500sin20 using the horizontal component of the applied force divided by the normal force, which was mg plus the vertical component of the applied force, but it didn't work, obviously. Any suggestions?
  2. jcsd
  3. Sep 11, 2007 #2


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    Your description seems right, but your numbers don't look right. The vertical component of the applied force is 700sin20... not 1500sin20
  4. Sep 11, 2007 #3


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    I'm not sure of your equations, but the force is applied below the horizontal; you seem to have assumed when calculating the normal force that the applied force is above the horizontal.
  5. Sep 11, 2007 #4


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    no, he assumed it was below the horizontal. He just used 1500 + 1500sin20 for the normal force, instead of 1500 + 700sin20.
  6. Sep 15, 2007 #5
    Yeah, I got that later. Thanks, though.
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