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Banked highway curves and static friction

  1. Feb 22, 2009 #1
    1. The problem statement, all variables and given/known data
    A 1200 kg car rounds a curve of radius 67 m banked at an angle of 12 degrees. If the car is traveling at 95 km/hr, will a friction force be required? If so how much and in what direction?


    2. Relevant equations
    F=ma
    a=v2/r

    3. The attempt at a solution
    I don't know what I'm doing wrong with this problem. These are the two equations I have from them and when I try to solve I either get a huge number or a negative.

    Ncos[tex]\theta[/tex]-Ffrsin[tex]\theta[/tex]-mg=0

    Nsin[tex]\theta[/tex]+Ffrcos[tex]\theta[/tex]=ma

    I'm positive that it needs friction force and I think it is in the direction of the center of curve, but I haven't figured out a way to solve. Can someone please help?
     
  2. jcsd
  3. Feb 23, 2009 #2

    Delphi51

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    Homework Helper

  4. Feb 23, 2009 #3
    Hey thanks! I think I found out what I was doing wrong. I didn't really take notice that the force of friction was equal to the friction coefficient multiplied by the normal force. Thank you very much!
     
  5. Feb 23, 2009 #4
    I don't think you did.
    Your equations were right but you need to solve for F by eliminating N.

    By far the simplest way is to resolve || to the slope in the first place.
     
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