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Homework Help: Car on unbanked curve

  1. Jul 5, 2004 #1
    I'm setting this problem up, but I'm now stuck.

    A car is safely negotiating an unbanked circular turn at a speed of 17m/s. The maximum static frictional force act on the tires. Suddenly a wet patch in the road reduces the maximum static friction force by a factor of three. If the car is to continue safely around the curve, to what speed must the driver slow the car?

    I made a free body diagram and came up with f net equations. I have fnetx=1/3usg=v^2/r. I have fnety=N-mg. For fnetx, I further get 3.267m/s^2us=v^2/r. And this is where I get stuck. I'm not sure what I do to find the speed without knowing the radius.
     
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  3. Jul 5, 2004 #2

    arildno

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    The magnitude of the initial frictional force satisfies:
    [tex]F=m\frac{v_{0}^{2}}{R}[/tex]

    Afterwards, we have:
    [tex]\frac{1}{3}F=m\frac{v_{1}^{2}}{R}[/tex]

    By division, we get:
    [tex]\frac{1}{3}=(\frac{v_{1}}{v_{0}})^{2}[/tex]
     
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