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Homework Help: What is the wavelength?

  1. Apr 11, 2012 #1
    1. The problem statement, all variables and given/known data
    Two sinusoidal waves with equal wavelengths travel along a string in opposite directions at 7.72 m/s. The time between two successive instants when the antinodes are at a maximum height is 0.324 s. What is the wavelength (in m)?


    2. Relevant equations
    vt=x
    Also,
    Propagation speed = wavelength * frequency = wavelength / period time


    3. The attempt at a solution
    I tried many, many different ways to solve this equation but ultimately I keep getting the wrong answer.. Here is one of the attempts:
    The distance between two successive antinodes or two successive nodes is equal to the wavelength of the wave. I figured out the distance based on the speed of the wave and the time between two antinodes with vt = x (since there is no acceleration).
    (7.72)(0.324)= 2.50128 m
    Yet it is not the right answer? Can anyone give me any more insight on what I can do..?
     
  2. jcsd
  3. Apr 11, 2012 #2

    BruceW

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    The question is a bit vague... does it mean both waves are moving at 7.72 m/s in opposite directions? so their relative velocity is 15.44 m/s ? And it seems to suggest standing waves, but it doesn't mention the end points of the string, so really the two waves could have any phase difference.

    If I was guessing, I'd say each of the waves is moving at 7.72 m/s so their relative velocity is 15.44 m/s and I'd guess the situation is standing waves caused by the string being fixed at one end. But what do you think? was there more information?
     
  4. Apr 11, 2012 #3
    Yes! :) I got the answer, the velocity was 15.44 m/s. Thanks!
     
  5. Apr 11, 2012 #4

    BruceW

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    alright, cool
     
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