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Homework Help: How long does it take to stop the car

  1. Jul 5, 2005 #1
    if a car is moving at 14m/s, and the coefficient of friction is 0.8, what is the distance it takes to stop the car after the brakes are applied locking all four wheels?
  2. jcsd
  3. Jul 5, 2005 #2
    The first step in the problem is to draw your free-body diagram and label all of the forces acting on the car.
    Basically you have 3 forces, the force of the weight, the force of friction, and the normal force on each tire.
    Because each of these forces are the same on each wheel it is only neccesary to draw the FBD for one wheel.
    After you draw your FBD set up your force equation in each direction. In this case the car is is only moving in 1 direction call it the positive X direction.
    So you have your sum of the forces in the X direction equation.
    where is the friction force

    solve that equation for a and then use the kinematic equation Vf^2=Vi^2+2*a*d

    with Vf=0 solve for d
  4. Jul 5, 2005 #3
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