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Speed of progressive waves numerical

  1. Jun 29, 2012 #1
    1. The problem statement, all variables and given/known data:
    progressive waves of frequency 300 hz are superimposed to produce a system of stationary waves in which adjacent nodes are 1.5m apart.calculate speed of progressive waves?


    2. The attempt at a solution:
    should i use
    1)v=f*λ=300m/s
    or
    2)v=f*(2λ)=900m/s
     
  2. jcsd
  3. Jun 29, 2012 #2

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    Be careful here.

    The symbol for wavelength is pretty much always denoted as λ. And the velocity of a wave is always v = λf (where f is the frequency). This relationship wasn't used correctly in 2), given your choice of variable names.

    (Not to mention that the math in 1 isn't right either; 300 x 1.5 ≠ 300)

    What you should be asking yourself is "how many nodes occur in one wavelength?"

    Try plotting cos x on a piece of paper. Don't forget to put the x-axis and y-axis on the plot. From one peak to the next peak of the function (one wavelength), how many times does the function cross the x-axis? :wink:
     
  4. Jun 30, 2012 #3
    sorry my bad @ 1.
    in 2, ive used 2λ because the distance between 2 consecutive nodes is λ/2..so used L=λ/2 or 2L=λ which results in 900 m/s..
     
  5. Jun 30, 2012 #4

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    That's good. :approve:
    Wait, you've determined a length. Just make sure you distinguish the difference between the wavelenth λ and the and the distance between nodes. Both are distances, but they are different distances.

    Once you've determined λ, v = fλ still applies. :smile:
     
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