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Homework Help: Finding car speed

  1. Oct 31, 2011 #1
    1. The problem statement, all variables and given/known data
    A race car starting from rest accelerates uniformly at a rate of [itex]4.90m/s^{2}[/itex] . What is the car's speed after it has traveled 200m?

    2. Relevant equations

    Δv = [itex]\frac{Change in position}{change in time}[/itex]

    3. The attempt at a solution
    v=[itex]\sqrt{980m^2/s^2}[/itex]

    =31.3m/s
     
  2. jcsd
  3. Oct 31, 2011 #2

    SammyS

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    Show your work so that we can help you see where your error is.

    How did you get [itex]v=\sqrt{980m^2/s^2}\,?[/itex]
     
  4. Oct 31, 2011 #3

    gneill

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    What kinematic formula are you using? It looks like you've missed out a constant.
     
  5. Nov 1, 2011 #4
    Well I'm required to find the speed after 200 meters, but I was never given any time.

    So I assume... Which is not a good thing to do, multiplying the acceleration * the distanced travel would give me the speed.

    But I really can't remember the actual equation.
     
  6. Nov 1, 2011 #5

    gneill

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    If you can't remember you should check your notes or text book! Your formula is close to being a valid kinematic expression,... but it's missing a constant. Do you have a list of the common kinematic expressions?
     
  7. Nov 1, 2011 #6
    I have the text book, and I did have an example sheet but my friend borrowed to check her work. I found this expression which seems to satisfy my problem, v2 = vo2 + 2a(X - Xo)

    Therefore V2= 0m/s + 2(4.90m/s^2)(200m)

    v2= 9.8m/s^2(200m)
    v2= 1960m^2/s^2
    v=[itex]\sqrt{1960m^2/s^2}[/itex]
    v= 44.3m/s
     
  8. Nov 1, 2011 #7

    gneill

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    That looks better :smile:
     
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