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Homework Help: Car on wet road

  1. Feb 7, 2006 #1
    A car is traveling at 46.0 mi/h on a horizontal highway.
    If the coefficient of static friction between road and tires on a rainy day is 0.101, what is the minimum distance in which the car will stop?

    Just confused on where to start becuase it seems like I need more info
  2. jcsd
  3. Feb 7, 2006 #2
    There is something missing. Don't you have a weight of the car ?

    You should apply :
    [tex]x = v_ot -a \frac{t^2}{2}[/tex]
    [tex]v = v_o -at[/tex]

    Where the v_o is initial velocity and a is the acceleration due to the friction. Beware of the sign !!!

    Solve the second equation for t (the v is zero when the car has stopped) and substitute this t in the first equation to solve it for x.

  4. Feb 7, 2006 #3
    Thats what I thought but there is no mass given
  5. Feb 7, 2006 #4
    ohh yes, just apply newton's second law in the vertical Y-direction :

    [tex]ma_y = 0 = N -mg[/tex]

    normal force N equals N = mg

    and friction force F = 0.101N = 0.101mg

    The associated acceleration is F/m = 0.101g and g=9.81 m/s²

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