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Homework Help: Length of Skid Marks

  1. Feb 27, 2009 #1
    1. The problem statement, all variables and given/known data

    A 1000 kg car traveling at a speed of 40 m/s skids to a halt on wet concrete where [tex]\mu[/tex]k = 0.60. How long are the skid marks?

    2. Relevant equations

    Vf = Vi + 2ad
    fk = [tex]\mu[/tex]kN = ma

    3. The attempt at a solution
    This problem is driving me crazy. Nowhere in the book does it tell you how to do this or even a similar problem. Plus, online, all I can find is how to find the speed once you've found the length of the skid marks! And yes, I tried doing the problem in reverse but the answer never comes out right.

    Here is what I've done.

    1000 * 9.8 = 9800
    9800 *.6 = 5880
    acceleration = 5880/1000 = 5.88

    0 = 40 + 2 * 5.88 * d
    d = 3.4

    I know I've done something incredibly wrong here because the answer in the back of the book is 136!

    I appreciate the help

    a(1000) = 5800
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 27, 2009 #2


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    Homework Helper

    That 40 should be squared!
  4. Feb 27, 2009 #3
    oh wow. thank you so much!
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