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Homework Help: Frictional Forces and 1D Motion

  1. Mar 13, 2007 #1
    This is a problem from my Introduction to Physical Science class using "Conceptual Physics" 10th Ed.by Paul G. Hewitt

    "The coefficient of kinetic friction between a rubber tire and a wet concrete road is 0.5."

    a) Find the minimum time in which a car whose initial speed is 30 mi/hr can come to a stop on such a road.
    b) What distance will the car cover in this time?

    I know I have a coefficient of friction & V0 and Vf. Beyond that, I don't know how to look for the time it will take. What equation am I supposed to be using?
  2. jcsd
  3. Mar 13, 2007 #2
    Lets take this a step at a time. To stop, you need a negative acceleration. Assume the brakes are aplied full force as in panic stop.

    I still find the fact that speed/velocity never enters the eqn curious: that is the braking force is constant. Whether from 100mph or 5mph the retarding force is the same. So its like a baseball thrown upwards at different speeds.:The stopping distance depends on velocity, but its predictable. This is key.

    So in a horizontal position, the frictional force depends on the negative force/acceleration generated by the weight times the coeffiecient of friction. Any help?
    Last edited: Mar 13, 2007
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