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Homework Help: Ap physics friction force please help

  1. Sep 28, 2013 #1
    Ap physics friction force please help!!!!

    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 the friction force is 6000N. How far does the car slide before coming to a stop?

    2. Relevant equations

    F=mv^2 / r
    1000 kg x (40 m/s^2) / r = 6000 N
    I got 266.7

    3. The attempt at a solution
    I came up with a positive number and it should be a negative number... What am I doing wrong?!
  2. jcsd
  3. Sep 28, 2013 #2

    Simon Bridge

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    Science Advisor
    Homework Helper

    Why would you expect a negative number?
    (And don't forget units.)

    F=mv^2/r is for centripetal force isn't it? Is the car going in a circle?
  4. Sep 28, 2013 #3
    Well..it always depends on which direction you choose to be positive and which negative.
    However, the equation you used wasn't correct. Think it in terms of work and energy.
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