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Homework Help: Finding original speed / acceleration

  1. Feb 6, 2006 #1
    Im new to this stuff so bear with me. I am really only looking for help as to what equation I use to find these answers.

    A truck covers 40.0m in 8.50s while smoothly slowing down to a final speed of 2.80 m/s.

    A. Find the trucks original speed.

    B. Find the its acceleration.
  2. jcsd
  3. Feb 6, 2006 #2
    try using solving for 2 variables, initial speed and acceleration, in 2 equations:
    x = v0*t + 1/2 *a*t2
    v2 = v02 + 2*a*x
  4. Feb 6, 2006 #3
    Im confused as to which is number is my accelartion and which is my velocity
  5. Feb 6, 2006 #4
    you know 3 variables, x = 40.0m, t = 8.50s, and v = 2.80m/s
    you need to find v0, the initial speed, and a, the acceleration

    use your knowledge of algebra to find these 2 variables in 2 equations
  6. Sep 19, 2008 #5
    Sorry to bring this post back from the dead -- but I'm doing this problem right now, and is V0 supposed to be 0? If I use formula VFinal: 2.80 m/s = V0 + AT (A being unknown at this point) and T being 8.5 seconds...

    I'm left with a mad scramble of algebra where V0 = .33m-A

    I'm constantly getting confused as to what to use when in these kinematics equations.

    a(acceleration) = Vf-V0/T

    a= 2.8m/s - V0 / 8.5 s

    How would I go about plugging that in...that would still leave me with two variables none of which I seem to be able to solve for.
  7. Sep 19, 2008 #6
    Is Vo supposed to be 40 m/ 8.5 s to get 4.71 m/s initial velocity?
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