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Problem with running car

  1. Aug 12, 2013 #1
    1. The problem statement, all variables and given/known data

    A car starts to run from rest with acceleration 0.5 m/s2. How long does it take to travel distance 60m? [sic] (I have a Russian teacher for AP Physics)

    2. Relevant equations

    V= (Xf-Xi)/(Tf-Ti)
    ΔX= Vi*T+(1/2)aT2

    3. The attempt at a solution

    I tried to find velocity, but that didn't really work out.
    0.5 m/s2=Vf-Vi/Tf-Ti
    Is there an equation or some way that I can directly solve for distance from acceleration?
     
    Last edited: Aug 12, 2013
  2. jcsd
  3. Aug 12, 2013 #2

    BruceW

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    Homework Helper

    ΔX= Vi*T+(1/2)aT2
    from this equation, you are close to the answer already. What does Vi stand for here? and so what is its value?
     
  4. Aug 12, 2013 #3
    Vi stands for initial velocity. It has an unknown value.
     
    Last edited: Aug 12, 2013
  5. Aug 12, 2013 #4
    What does "A car starts to run from rest" mean to you with regard to the car's initial velocity?
     
  6. Aug 14, 2013 #5
    I got it in class. :frown:

    This was the process:

    (Vf-Vi)/(Tf-Ti)=A

    Or rather... ΔV/ΔT=A

    Since A= 0.5 m/s2, A=(0.5 m/s)/1 s

    Thus, V= 0.5 m/s

    The ratio is the same and thus (0.5 m)/(1 s)=(60 m)/(x s)

    60 m*s = 0.5x m*s

    120 s

    :P

    Thank you for putting up with me and with the odd grammar.
     
  7. Aug 14, 2013 #6

    gneill

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    Staff: Mentor

    That can't be right. After 120 seconds with an acceleration of 0.5 m/s2 the car will have traveled 3.6 kilometers...that's more than slightly larger than 60 m.

    What you've sort of calculated is the time it takes for the velocity to reach 60 m/s. Unfortunately, velocity is not the same as distance :smile:

    Go back to your second equation (the one for ΔX) and take another look at the posts by BruceW and Chestermiller.
     
  8. Aug 14, 2013 #7

    SteamKing

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    Science Advisor
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    How fast do you run when you are at rest?
     
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