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Posted by on Wednesday, October 28, 2009 at 1:45am.

A 1500kg car skids to a halt on a wet road where μk= 0.53. How fast was the car traveling if it leaves 62-m-long skid marks?

  • Physics - , Tuesday, October 7, 2014 at 8:10pm

    First draw a free-body-diagram with Fn (normal force) pointing upward mg(Fg) pointing downward and the force of friction Ff to the left. Then set your axis for this problem I choice up and to the left as positive.

    So you use Newtons 2nd law to find Fn
    So the summation of Fy=ma
    Since there is no motion in the y direction a=0
    So it is Fg-ma so it's Fg=ma and it's (1500)(10) which gives you 15000N

    Then you find Ff
    Ff=u(mew)Fn
    Ff=(.5)(15000)
    Ff=7500N

    Then you use F=ma because you are trying to find acceleration in the x direction which means you have to use the Ff because it is in the x direction so you get :
    A=Ff/m
    A=5 m/s^2

    Then you need to find the initial velocity Vi so use
    Vf^2=Vi^2 + 2ad
    Vf=0 because it skids to rest so
    0=Vi^2 + 2ad
    -2ad=Vi^2
    When you work all of it out you get -25.5 m/s it something around there

    Hope this helped

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