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Homework Help: 1d motion question

  1. Sep 9, 2012 #1
    1. The problem statement, all variables and given/known data
    at the instant the traffic light turns green, s starts from rest and accels at a_s. at the same time k passes s with constant velocity v_k.

    given a_s, v_k,
    find distance before the cross again
    time it takes to do so
    velocity of s at this point

    plot the position as a function of time for both. take x=0 at the intersection <- no idea what last sentence means.

    2. Relevant equations
    v_s = a_s + t
    d = 1/2 a_s * t^2
    v_s^2 = 2a_s*d

    d= v_k * t


    3. The attempt at a solution

    t = sqrt(2*v_k/a_s)
    d = v_k * sqrt(2d/a_s)
    v_s = a_s*sqrt(2d/a_s)


    as for this plotting, does this mean I "start" the graph at their intersection? which one?
     
  2. jcsd
  3. Sep 9, 2012 #2
    as for this plotting, does this mean I "start" the graph at their intersection? which one?
    ..........................................................
    Yes.
    k with constant velocity-a straight line.
    s with constant acceleration- a parabola.
     
  4. Sep 9, 2012 #3

    TSny

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    I think the "intersection" is the intersection of the streets where the traffic light is positioned. So, take x = 0 to be the location where k initially passes s.
     
  5. Sep 9, 2012 #4
    wanted to be sure, thanks.
     
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