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Homework Help: Finding the complex amplitude

  1. Sep 1, 2008 #1
    1. The problem statement, all variables and given/known data
    i gotta find the complex amplitude
    i know that w = 50Hz
    displacement was 30mm at time 0
    and -14mm at time 12ms

    2. Relevant equations

    (displacement) = Acos(phase constant)cos(wt) - Asin(phase constant)sin(wt)

    3. The attempt at a solution
    so ive tried plugging things in to the expanded wave equation
    and just plugging things in for t = 0
    which gives me the correct answer Acos(phase constant) = .03 at time 0
    but when i try the second time to get the sin phase constant, it gives me .068
    but my answer is supposed to be
    .03 +.0175 i
    what am i doing wrong?
    which equation could i use?
    any help would be appreciated
  2. jcsd
  3. Sep 1, 2008 #2
    nvm figured it out
    i was using 50 hz as my w
    but really its my v
    and i had to convert it with v = w/2pi
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