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Homework Help: Vector dynamics question starting from accelaration

  1. Sep 27, 2010 #1
    1. The problem statement, all variables and given/known data
    I took this right out of the text, it is not home work just me trying to get better.

    The acceleration of a particle is defined by the relation a = -8 m/s^2
    Knowing that x = 20 m when t= 4 m, and that x = 4 m when v = 16 m/s
    (a) determine the time when velocity is zero and (b) the velocity and total distance travelled when t = 11 s

    2. Relevant equations

    3. The attempt at a solution
    My attempt is I know velocity must be the integration of acceleration and displacement the integration of velocity. So I attempted to integrate -8dt 2 times. but when I do that I get x=-4t^2 which does not fit my given when t=4, x=20
    Any help would be greatly appreciated, even just pointing me in the right direction
  2. jcsd
  3. Sep 27, 2010 #2


    User Avatar

    Looks like you need to take initial conditions into account. Remember that when you integrate you have a constant of integration as well, which you can determine if you have initial conditions (which you have).
  4. Sep 28, 2010 #3
    How do I know which of the conditions to use for the initial conditions?
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