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Homework Help: Kinematic Problem

  1. Feb 28, 2005 #1
    Hi,really need help with this question.
    A motorist travelling at 13 m/s aprroaches traffic lights which turn red when he is 25m away from the stop line.His reaction time(i.e. the interval between seeing the red light and applying the brakes)is 0.7s and the condition of the road and his tyres is such that the car cannot slow down at a rate of more than 4.5 ms-2.If he brakes fully,how far from the stop line will he stop,and on which side of it?

    Thanks in advance!
  2. jcsd
  3. Feb 28, 2005 #2
    Please show us some effort from u! It is not that we cannot give you help.
  4. Feb 28, 2005 #3
    use the very simple kinematics equations available. Manipulate them to et an answer. If you have a more specific probem in this question, please state it. Nobody will solve your problem for you.

    [tex] V^2 = {V_o}^2 + 2ad [/tex]
    [tex] d = V_o t + \frac{1}{2} at^2 [/tex]
    [tex] V = \frac{d}{t} [/tex]


  5. Feb 28, 2005 #4
    Oh,sorry,I actually just have one problem,which is the acceleration part of the question.Can anyone just explain what it means?Thanks.
  6. Feb 28, 2005 #5


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    It's a deceleration.With constant acceleration [itex] a=-4.5ms^{-2} [/itex]...

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