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Homework Help: Kinematics decelerating

  1. Oct 24, 2011 #1
    A train approaches a small town with a constant velocity of +28.6 m/s. The operator applies the brake, reducing the train’s velocity to +11.4 m/s. If the average acceleration of the train during braking is –1.35 m/s^2, for what elapsed time does the operator apply the brake?

    2. i tried to use the equation for definition of acceleration

    3. i set up my diagram and my question is; what is the initial velocity when the operator starts applying the brakes?
  2. jcsd
  3. Oct 24, 2011 #2

    The train is traveling at 28.6m/s when it starts to experience a negative acceleration of 1.35m/s^2 until it is traveling at 11.4m/s

    So initial velocity is 28.6, final velocity is 11.4 and acceleration is -1.35

    Just look at your kinematics equations, you should be able to use

    Vf = Vo +at
  4. Oct 24, 2011 #3
    why wouldn't the final velocity be 0 m/s
  5. Oct 24, 2011 #4
    Why would it be? The train is starting at 28.6m/s and ending up at 11.4m/s so final velocity is 11.4

    The final velocity would be zero if the train came to a stop, but it doesn't.
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