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Help needed ><

  1. Nov 16, 2003 #1
    help needed!!!! ><

    Someone plz help me with this question!!!
    (at least show me how to do it~!)

    A car slams on its brakes and skids to a halt from 65km/h in 2.67s. Find the coefficient of friction between the car tires and the road.

    Thanks in advance~! ^^
     
  2. jcsd
  3. Nov 16, 2003 #2

    HallsofIvy

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    You know the change in speed in a given time (65km/h in 2.67s) so you can find the acceleration. IF you knew the mass of the car, then you could calculate the friction force from F= ma.
    Since you are asked for the "coefficient of friction" rather than the friction force itself, you don't need the mass: The friction force is F= k*weight= kmg.

    That is, F= ma= kmg so k= a/g- the mass cancels out.
     
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