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Calculate force of friction using tension & angles

  1. Feb 22, 2009 #1
    1. The problem statement, all variables and given/known data
    A 60 kg crate is being steadily dragged along the floor by a rope, which makes an angle of 70 degress with the horizontal. If the tension in the rope is 20N:
    What is the force of friction?
    What is the coefficient of friction?

    2. Relevant equations

    ffr=Ufn
    ffr=Umgcos0


    3. The attempt at a solution

    i know that
    fg=mg
    = 60(9.8)
    =588N

    and
    Fn= fgcos70
    =588cos70
    =201N

    i dont knwo what to do from there
     
  2. jcsd
  3. Feb 22, 2009 #2
    anyone?
     
  4. Feb 22, 2009 #3
    I'm not sure why your normal force is Fg*cos(70). From my diagram, I get the force of friction |Ff| = |Fg| - |T|sin(70) where T is the tension.
     
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