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Kinematics Equation Proof

  1. Aug 7, 2016 #1
    1. The problem statement, all variables and given/known data

    Eliminate t from the equation (x-xi)=vi(t)+1/2(a)t^2 using the kinematic equation v=vi+at to get
    v^2=vi^2+2a(x-xi)
    3. The attempt at a solution
    I wind up with (x-xi)=vi(v-vi/a) + 1/2(v^2-vi^2/a). If the first term on the right side didn't exist, I could see what the solution is, but I can't see why it just seems to disappear.


    here is a video showing the exact step where I get lost. Again, the first term on the right just disappears. I can see why that would happen if the initial velocity is 0, but what if it isn't?
     
    Last edited: Aug 7, 2016
  2. jcsd
  3. Aug 7, 2016 #2

    haruspex

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    You've marked several places in the video. Not sure which step is bothering you.
    It might be more useful to post your own working.
     
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