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Homework Help: Quick question about instantaneous velocity and acceleration

  1. Jul 15, 2016 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations


    3. The attempt at a solution

    Hey, I did part a and b. Although I need a little help with part c.
    I know you're supposed to solve for t^2 but I don't know what value to use for acceleration.
    I'd use the quadratic formula to solve for t^2, but I'm just not sure which values to use...
    At first I thought the initial velocity would be zero and the acceleration would be zero but then that left me with:

    -1/2 * (4.8 m/s^2) = 0 which doesn't lead to the right answer. Could you guys point me in the right direction?
  2. jcsd
  3. Jul 15, 2016 #2
    I ended up just differentiating then doing 0.36T^2 - 4.8T = 0 ---> (0.36T^2) / (0.36T) = (4.8t)/ (0.36T) which gave the right answer, but I wanted to know if there was a way to use the quadratic formula and the above equation since that's how the example in the book was done. I guess at this point its kind of an algebra question than a physics question.
  4. Jul 15, 2016 #3
    You can't use the one dimensional equation you have given in the first post as in this case the acceleration is not constant.
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