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Coefficient of static & kinetic friction

  1. Sep 22, 2009 #1
    1. The problem statement, all variables and given/known data
    If the force needed to start the motion of an object having a mass of 2.5 kg is 4.90 N, what is the coefficient of static friction?

    2. Relevant equations
    f = uN
    Since u is missing, the formula is u = f/N

    3. The attempt at a solution
    u = 4.90 N/(2.5 kg X 9.8 m/s2)
    u = 4.90 N/24.5 N
    u = 0.2

    The problem is asking for the coefficient of static friction. I'm not sure if I got the answer for kinetic friction? I know the difference between the two but I don't know why the problem required static friction when it is talking about a moving object.
     
    Last edited: Sep 22, 2009
  2. jcsd
  3. Sep 22, 2009 #2
    When an object is at rest it will have static friction and kinetic friction when it is moving. So in order to move an object, you will need to overcome the static friction.
     
  4. Sep 22, 2009 #3
    Thanks semc. But is my solution correct?
     
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