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Homework Help: Need help finding Kinematic formula for Initial V

  1. Sep 10, 2009 #1
    1. The problem statement, all variables and given/known data
    A truck covers 60.0 m in 9.0s while smoothly slowing down to final speed 3.00 m/s.
    Find the initial velocity.

    2. Relevant equations
    Vi +1/2at^2 has two unknowns
    V= vo + at has two unknowns
    x= v^2 - Vi^2/2a has two unknowns
    v^2=vi^2 +2a(xf-xi) has two unknowns

    3. The attempt at a solution
    I have been scouring the internet looking for a formula that can solve for V initial excluding acceleration that can work! I can't seem to find any! How do I go about finding the initial velocity?
  2. jcsd
  3. Sep 10, 2009 #2
    Variables you have: final velocity v, displacement s, and time t. Which one of the four classic kinematics equations excludes the acceleration a?
  4. Sep 10, 2009 #3
    I can't believe I overlooked that! Thank you!
  5. Sep 10, 2009 #4


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    Homework Helper

    You have to use two equations
    vf = vi - at.......(1)
    x = vi*t - 1/2*a*t^2 ......(2)
    substitute the value of vi from the first equation in the second equation and solve for vi.
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