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Homework Help: Finding group velocity and Phase velocity

  1. Sep 18, 2012 #1
    1. The problem statement, all variables and given/known data

    A wave packet in a dispersive medium is given as :
    y(t) =cos(x-5t)cos(.2x-.4t)cos(.1x-.2t)
    Find group velocity and phase velocity for the wave packet. Hence plot w-k variation for the calculated values.

    2. The attempt at a solution

    We know that for the wave, Vg = dw/dk and Vp=w/k.

    I am clueless on how to proceed from here. Does the cosine term with lowest 'w' acts as the the modulating part? Please enlighten me with the correct information. It's not homework question, I'm trying this on myself so I may miss some critical information on how to approach it. Thanks! :)
  2. jcsd
  3. Sep 19, 2012 #2
    Bump Please!
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