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When is the particle speed up/slowing down

  1. Mar 21, 2009 #1
    1. The problem statement, all variables and given/known data

    The postion of a particle is given by s=2t^2-9t^2 where t is in seconds and s in meters

    a) when is the particle speeding up/slowing down

    2. Relevant equations



    3. The attempt at a solution

    I have calculated the
    1st derivative (velocity) as 6t^2-18t
    2nd derivative (acceleration) as 12t-18

    and I know that the particle is speeding up when the velocity and the acceleration have the same sign and slowing down when they have opposite signs. However I am not sure how to express this to answer the question.

    Thanks
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Mar 21, 2009 #2
    Find the values of t for which the velocity and for which the acceleration is positive/negative. Hint: They can only change sign at the zeros.
     
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