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Homework Help: Static Friction on a Curve

  1. Mar 2, 2010 #1
    1. The problem statement, all variables and given/known data

    If a curve with a radius of 87.5 m is perfectly banked for a car traveling 71.8 km/hr, what must be the coefficient of static friction for a car not to skid when traveling at 93.8 km/hr?

    2. Relevant equations

    tan [tex]\theta[/tex] = [tex]v^{2}[/tex] / r*g

    3. The attempt at a solution

    I found the banking angle:

    tan [tex]\theta[/tex] = 19.9^2 / 87.5 * 9.81 = 24.7 deg.

    But I'm not sure on how to find what the question is asking for. Help?!
  2. jcsd
  3. Mar 2, 2010 #2


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    Science Advisor
    Homework Helper
    Gold Member

    If there were no friction, would the car at that speed slide up or down the incline? The answer gives you the direction of the frictional force that is needed. Once you have the direction, draw a free body diagram and require that the acceleration have no vertical component.
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