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Homework Help: Traffic signal physics problem

  1. Sep 3, 2005 #1
    this is a problem I have . But because I cannot include the graph, I try to do via Microsoft Word. I put it as an attachment. I hope that you will understand it.

    This is the problem:

    Traffic signals are placed along a straight road at positions x = 0 m, x = 600 m, and x = 1200 m (see graph in attachment)). The time intervals during which the signals are green are shown by the thick lines ( in red) in the figure.

    (a) Draw the displacement-versus-time curves (fastest and slowest) for a car that passes through all the lights when the car moves with constant speed.

    (b) Draw a similar set of lines for a car traveling in the opposite direction.

    (c) Assuming that the lights are timed such that a car passes through all lights in the middle of the time interval, what is the speed for which the lights are timed?

    (d) What is the fastest constant speed of a car that makes it through all the signals, assuming it arrives at the first light at the optimal moment?

    For info.:
    The grah is a 2 dimension space with time(s) on horizontal and the position x(m) in vertical.
    The interval are put in red and I mentioned the time interval at the end of each line.
    Please help me with that . I do not understand it

    Thank you very much.


    Attached Files:

  2. jcsd
  3. Sep 3, 2005 #2


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    Staff Emeritus
    Science Advisor

    Well if you map x=x(t), then v = dx/dt and the slope is speed (or magnitude of velocity).

    If you draw a straight line, it's slope will be a constant speed.

    So the fastest speed, will have the steepest slope.
  4. Sep 3, 2005 #3

    Thank you that make more sense now , but what about quesion c

    I do not understand this question .

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