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Homework Help: Finding length of skid marks using f k

  1. Oct 6, 2009 #1
    Finding length of skid marks using fk

    1. The problem statement, all variables and given/known data

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

    (i know this an easy problem, but i am stuck when trying to find the length of the skid marks.)

    2. Relevant equations

    Fg = mg = weight = normal force

    fk = µkFN

    3. The attempt at a solution

    Fg = 1000(9.8) = 9800 N, therefore the normal force = 9800N
    µk = .60

    fk = .60(9800)
    fk = 5800 N

    v0 = 40m/s
    fk = 5880 N

    Where do i go from here to find the distance of the skid marks?

    i was thinking maybe using the formula, x = x0 + vt, but i am not sure
  2. jcsd
  3. Oct 6, 2009 #2


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    Welcome to PF!

    Hi physjeff12! Welcome to PF! :wink:
    From fk, find the acceleration, and then use one of the standard constant acceleration equations. :smile:
  4. Oct 6, 2009 #3
    Re: Welcome to PF!

    thanks :smile:

    and how do i find the acceleration using fk? i don't know any formulas that connect acceleration with friction force.

    EDIT: nvm, i am stupid. i found out how. F = ma :smile:
  5. Oct 6, 2009 #4


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    Friction is like any other force …

    just use good ol' Newton's second law. :wink:
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