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Sinusoidial waves: Frequency is not dependant on speed?

  1. Feb 25, 2013 #1
    1. The problem statement, all variables and given/known data

    I am really confused.

    v = λ f

    doesn't that imply that speed is dependent on frequency?

    There is a question in my book that says:

    A sinusoidal wave of frequency f is traveling along a stretched string. The string is brought to rest, and a second traveling wave of frequency 2f is established on the string.
    (i) what is the wave speed of the second wave?

    2. Relevant equations

    v = λ f

    3. The attempt at a solution

    so I figured the answer would be something like:

    since v1=λf
    it follows that, if the second wave has frequency 2f
    v2 = λ(2f)
    v2 = 2 (λf)
    v2 = 2 (v1)

    but somehow the answer is: "the same as the first wave" Can someone explain this to me?
  2. jcsd
  3. Feb 25, 2013 #2


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    Science Advisor
    Homework Helper

    You are assuming λ doesn't change. You have the wrong equation. What equation determines the speed of a wave on a stretched string? Might just involve tension and mass density, yes?
  4. Feb 25, 2013 #3
    Ohhhhh, right right. If frequency increases λ would get shorter.

    i flipped two pages down and found:

    problem solved. Thanks.
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