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Homework Help: Kinematics problem

  1. Sep 24, 2011 #1
    1. The problem statement, all variables and given/known data


    I've attempted this problem for just Laura so far.

    t1 = 2.00s
    t2 = 10.4s - 2.00s = 8.40s

    vi = 0.0m/s
    vf at the end of 2.00s = vmax

    For her displacement I have a little diagram:

    ........x..............xf = 100 - x.....

    where the split between the two sections occurs at whatever x is after 2.00s.

    a=? for the initial time interval from 0.00s to 2.00s.
    a=0 from 2.00s to 10.4s.

    2. Relevant equations

    For constant velocity: xf = xi + v*t

    For constant acceleration:


    3. The attempt at a solution

    From t=0.00 to t=2.00:

    (using eq'n 2.15, where xf=x, xi=0, vxi=0, and t1 = 2.00)

    x = 0.5 * v * t2
    x = 0.5 *v*2.00
    x = v (???)

    From t=2.00 to t=10.4:

    (using constant velocity equation, where xi=0, and xf = 100 - x, and t2=8.40)

    100 - x= v * t2
    100 - x = v*8.40

    And basically when I equate the two equations I don't get the right answer (which is a=5.32m/s...). Help!
  2. jcsd
  3. Sep 24, 2011 #2


    User Avatar
    Homework Helper

    All your work looks correct - I don't know how you missed the final answer. You have that the distances for the two parts are v and 8.4*v.
    So v + 8.4*v = 100. That works out to v = 10.6.
    a = Δv/Δt = 10.6/2 = 5.3 m/s².
  4. Sep 25, 2011 #3
    God Da-...Ugghh.

    Well then. Frustrating, but I guess it feels good to know I had it all along haha.

    Thank you :)
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