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Parts of a Wave

  1. Dec 6, 2009 #1
    The displacement of a wave traveling in the positive x-direction is y(x,t) = (3.5 cm)cos(2.7x - 124t), where x is in m and t is in sec. What are the (a) frequency, (b) wavelength (in m), and (c) speed (in m/s) of this wave?

    I don't know how to do this problem at all. I could use some help beginning and solving this problem. Thanks. I don't know how to do harmonics very well.
  2. jcsd
  3. Dec 6, 2009 #2


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    Homework Helper

    For starters, what do you know about frequency, wavelength, and speed in general?
  4. Dec 6, 2009 #3
    They are all linked in the equation:

    v = [tex]\lambda[/tex]f
  5. Dec 6, 2009 #4
    The only thing I don't get is how to find any of them if they are all linked with one equation.
  6. Dec 6, 2009 #5
    Well, after doing the math (considering I did this right, or I hope I did), I got:

    y(x,t) = Acos((2[tex]\pi[/tex]/[tex]\lambda[/tex])x [tex]\pm[/tex] (2[tex]\pi[/tex]/T)t)

    which led me to

    (a): 124 = 2[tex]\pi[/tex]/T
    T = 2[tex]\pi[/tex]/124 = .05067

    f = 1/T = 1/.05067 = 19.74

    (b): 2.7 = 2[tex]\pi[/tex]/[tex]\lambda[/tex]
    [tex]\lambda[/tex] = 2[tex]\pi[/tex]/2.7 = 2.33 m

    (c): v = [tex]\lambda[/tex]f
    v = (2.33 m)(19.74) = 45.99 m/s

    Please tell me if and where I am wrong, or tell me if that is correct. Bold are the answers.
  7. Dec 6, 2009 #6
    That's what I got!
  8. Dec 6, 2009 #7
    Well, do you think we are right? I sure as heck hope so!
  9. Dec 6, 2009 #8
    Haha, yeah, we're right.
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