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Homework Help: Speed of a Particle

  1. Feb 12, 2009 #1
    1. The problem statement, all variables and given/known data

    Consider the following position function.
    r(t)= et(cos(t)i+sin(t)j+7tk)

    Find the speed of a particle with the given position function.

    2. Relevant equations

    I know I take the derivative of the function but I cant seem to get speed.
    I got v=e^t(cos(t)i+sin(t)j+7(t)k)+ e^t(-sin(t)i+cos(t)j+7k)

    3. The attempt at a solution

    I just cant find the speed, i think i may be just slightly off. I currently have speed is 7e^t(t+1) which is wrong.
  2. jcsd
  3. Feb 12, 2009 #2

    You are simply using "k" part, where is your i and j part. They don't cancel out.
    Last edited: Feb 12, 2009
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