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Homework Help: Acceleration problem

  1. Feb 1, 2008 #1
    1. The problem statement, all variables and given/known data

    A sports car accelerates from rest to 100km/hr in 6.2s. What is it's acceleration in m/s^2?

    2. Relevant equations

    3. The attempt at a solution
    I converted the 100 km/hr to m/s and got 16.7 m/s. I think that the formula that I am supposed to use is Vf-Vo/t. I don't know what to do next or if even what I did is correct.
  2. jcsd
  3. Feb 1, 2008 #2


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    100 km/hr=(100x1000)meter/60min=(100x1000)meter/(60x60)sec=27.8meter/sec.

    Now look at the units for acceleration. This should tell you what you must do with velocity(m/s) to get m/s^2.
  4. Feb 1, 2008 #3
    100 kM/hr = 27.78 m/s not 16.7 m/s. Look in your book. You should find a reference equation that looks something like v=at+vo. Since you know v0=o at time=0 the equation becomes simple. Now solve for acceleration since you have been given both the time and final velocity.

    Hope this helps.
  5. Feb 1, 2008 #4
    since 100km/h = 27.8 m/s

    use v^2 = V0^2 + 2a(y-y0)

    27.8^2 = 0 + 2a(y) ; 2 unknowns
    /////(27.8^2) / 2a = y

    then use y = y0+v0T+.5aT^2
    plug in with the Y you solved for in the other equation.
    772.84 / 2a = 0 + 0T + .5aT^2
    remember t = 6.2
    solve for a; a = 4.48 m/s^2

    check my math, i dont know
    Last edited: Feb 1, 2008
  6. Feb 1, 2008 #5


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    You are making it too complicated. You have one equation with one unknown: v=at+vo
  7. Feb 3, 2008 #6
    I'm not sure if I exactly understand. I understand a little more than I did before. It is hard for me because my class does not use a book and we have one practice problem as our notes.
    Last edited: Feb 3, 2008
  8. Feb 3, 2008 #7


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    This (Vf-Vo/t) is what you showed in your first post for finding the acceleration a. And as Newton1Law wrote, "Since you know v0=o at time=0..." then a=Vf/t. That's all there is to it.
  9. Feb 3, 2008 #8
    Thank you. That makes sense to me now.
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