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Finding the velocity of a standing wave

  1. Apr 27, 2013 #1
    1. The problem The distance between two consecutive nodes
    of a standing wave is 21.9 cm. The hand generating the pulses moves up and down through
    a complete cycle 3.72 times every 4.22 s.
    Find the velocity of the wave.
    Answer in units of m/s



    2. Some relevant things to know are:
    • Frequency equals the number of vibrations a wave makes per second
    • to measure the wavelength of a wave, you must have the length between either: A) two antinodes (peaks,trofts,crests,etc.) or B) THREE nodes. Since we only know the lenght between two nodes, it is assumed that we can multiply the distance (21.9 cm) by 1.5 to figure out the distance between three nodes.
    • and finally, once you determine both the frequency and the wavelenght, you must know how to deduce the velocity out of both. the equation for that is v=fλ




    3. Attempts I have attempted this problem several times using the above equations and methods. I came upon the answer 28.9578199052 m/s (≈29m/s) but apparently that is wrong.


    Thank you for any help you can provide, cheers!

    Edit: my sincere apologies for butchering the template, sorry, I'm new here!
     
    Last edited: Apr 27, 2013
  2. jcsd
  3. Apr 27, 2013 #2

    TSny

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    Hello and welcome to PF!

    How is the wavelength related to the distance between two consecutive nodes?
     

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  4. Apr 27, 2013 #3
    My physics teacher taught us that you can measure wavelength by finding the lambda values. So we count 1λ, 1.5λ, 2λ. etc. etc. Then we use the equation (#λ)(λ)=length of wave segment. Three nodes would be one lambda value and two antinodes would be one lambda segment.
     
  5. Apr 27, 2013 #4
    Be careful of your units also.
     
  6. Apr 27, 2013 #5

    TSny

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    What is the distance in cm between nodes N1 and N2? Between N1 and N3? What is the wavelength in cm?
     

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    Last edited: Apr 27, 2013
  7. Apr 27, 2013 #6
    In physics, to be safe, use meters not cm. There are many constants in physics that assume you are using mks units, i.e. meters, kilograms, and seconds. Recall in chemistry you might use cgs units, centimeters, grams, and seconds.
     
  8. Apr 28, 2013 #7


    Ah yes, this is probably the one thing I always over looked, units!

    Thank you, I'm gonna try it again later!
     
  9. Apr 28, 2013 #8
    Yah, I just realized that my main issue was mixing up centimeters with meters. I found the velocity as cm/s but overlooked it and entered it as m/s.
     
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