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Homework Help: Runner Runs

  1. Sep 14, 2016 #1
    1. The problem statement, all variables and given/known data
    In a 100 m sprint a runner starts from rest and accelerate to 9.6 m/s [W] in 4.2 s.
    Calculate acceleration, displacement, and if the runner runs at a constant velocity for the rest of the race what is the total time?

    2. Relevant equations

    3. The attempt at a solution
    I am having trouble with the total time. I know acceleration is 2.3 m/s^2 [W] and I know displacement is 20.16 m [W]. However what would the constant velocity be.. Is it 9.6 m/s[w]? And since it states the rest of the race does that mean i have to subtract 20.16 from the 100m?
  2. jcsd
  3. Sep 14, 2016 #2
    So what I did was take 100 subtract 20 to obtain 80. Then I took 80 divided it by 9.6 took that number and added 4.2 seconds to get the total time. The total time is 13s.. Can someone tell me if I did this correctly?
  4. Sep 14, 2016 #3


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    Looks good.
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