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Trajectory help

  1. Feb 15, 2009 #1
    A particle's trajectory is described by x=((1/2)t^3 - 2t^2) and y=((1/2)t^2-2t) , where t is in s.

    What is the particle's speed at t= 4.5 s?
    What is the particle's direction of motion, measured as an angle from the x-axis, at t=4.5 s?

    I keep geting the wrong answers >:0 , how do I go about solving this?
  2. jcsd
  3. Feb 15, 2009 #2


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    Gold Member

    How did you try solving this? Show us so we can explain where you went wrong.
  4. Feb 15, 2009 #3
    Take the derivative of both.

    Then solve for t = 4.5s, us these vector components to find the angle.
    Last edited: Feb 15, 2009
  5. Feb 15, 2009 #4
    Alright, so i dont know why I wasnt getting the right answer before(i was taking the derivatives), but I took the derivatives for x and y, then used the sqrt(x^2+y^2) to get part one. Then y=cos^-1(x/v) for part two.
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