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Calculating Force of Friction

  1. Oct 22, 2007 #1
    1. The problem statement, all variables and given/known data

    A car of weight 1500 N has its brakes locked. Calculate the force needed to begin to drag he car on dry asphalt. How will the force needd to slide it along the asphalt compare with the force needed to start sliding it? Why? (Static coefficient=1.2, Kinetic coefficient=0.8)

    Known: weight (1500 N, the mass in N on earth) , coefficients of static and kinetic friction

    2. Relevant equations

    Ff = (coefficient of kinetic)(normal force)
    Fn = mg

    3. The attempt at a solution

    (force needed to start it moving)
    Force of friction = 1.2 * 1500 N
    = 1800N

    (force needed to keep it moving)
    = Force of friction * coefficient Kinetic friction
    = 1800N * 0.8
    = 1440N

    Now that I have these numbers, I do not know what to write to answer the questions that are asked.
     
  2. jcsd
  3. Oct 22, 2007 #2
    I dont understand why you did 1800*0.8 for the second part. Should it not be 1500*0.8?

    Ffr=uFN
     
  4. Oct 23, 2007 #3
    These numbers tell you that you need a greater force to get the car sliding than you need to keep it sliding.
     
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