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Motion problem for constant acceleration

  1. Sep 20, 2010 #1
    1. The problem statement, all variables and given/known data
    A pedestrian is running at his maximum speed of 6.0 m/s trying to catch a bus that is stopped at a traffic light. When he is at 16 m from the bus, the light changes and the bus pulls away from the pedestrian with an acceleration of 1.0 m/s2.

    Does the pedestrian catch the bus and, if so, how far does he have to run? (If not, what is the pedestrian's distance of the closest approach?)


    2. Relevant equations
    d = vi * t + 0.5 * a * t2


    3. The attempt at a solution
    I don't understand how to do it :frown:
     
  2. jcsd
  3. Sep 20, 2010 #2

    collinsmark

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    Show us your best try. :biggrin: What is your equation for the displacement of the bus, from the traffic light, as a function of time t? What is your equation for the pedestrian's displacement from the traffic light as a function of time t? Is there ever a real-valued, positive time t where the displacements are equal? :wink:

    Hint: there's a more general equation that you might consider using, instead of the one you quoted (and don't forget the bus and the pedestrian each have their own individual velocities and accelerations):

    d = di + vit + ½at2
     
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