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I have a wave problem!

  1. Sep 16, 2012 #1
    I've never taken physics before and this is my first physics class in university.

    1. The problem statement, all variables and given/known data
    A string, 2.0 meters in length, is fixed at both ends and tightened until the wave
    speed is 78 m/s. What is the frequency of the standing wave shown in the figure?


    2. Relevant equations
    v=nv/2L because it is fixed at both ends


    3. The attempt at a solution
    so f = (78m/s)/(2)(2)
    and I get 19.5 Hz but that's not the right answer. It's too small. Help please?
     
  2. jcsd
  3. Sep 16, 2012 #2
    It seems like theres some information missing in your outline of the problem. Perhaps try multiplying by an integer, n, that is the number of wavelengths the standing wave is comprised of.
     
  4. Sep 16, 2012 #3
    Okay I actually just tried that. Here's the picture to the problem:

    ScreenShot2012-09-16at80313PM.png

    I thought the number of wavelengths was 6, but that doesn't seem to be right? Am I reading the picture wrong?
     
  5. Sep 16, 2012 #4
    Theres only 3 wavelengths in that picture;)
     
  6. Sep 16, 2012 #5
    haha okay I see that now. So then I'd do

    f = (78m/s)(3m)/(2m)(2)

    and I'd get 58.5 which doesn't make sense. my answer either has to be A) 350Hz B) 230Hz C) 120Hz D) 470Hz and it's neither. so is my formula wrong maybe? because isn't frequency supposed to have units s? because that gives me units m/s.
     
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