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Homework Help: Velocity of sound in Carbon Diox vs. Air

  1. Mar 29, 2010 #1
    1. The problem statement, all variables and given/known data

    An organ pipe is blown with carbon dioxide and produces waves 2 ft long and a note with a frequency if 350 Hz. What is the velocity of sound in carbon dioxide? How do you account for the fact that this is not the same as the velocity in air?

    2. Relevant equations

    Wavelenght=velocity/frequency therefore Velocity=wavelength*frequency.

    3. The attempt at a solution
    Velocity =2ft*350HZ=213.36 m/s

    My teacher wants the answer in the same units as the question, but 700 ft/Hz doesn't seem like a true meausrement? Which is why I put 213.36 m/s? I am on track here?

    Also, would this velocity be different than that of air b/c carbon dioxide is heavier and denser than air?
  2. jcsd
  3. Mar 30, 2010 #2
    Yes and that is because v = sqrt( krt/m0) where k stands for adiabatic exponent.
  4. Mar 30, 2010 #3


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    What's wrong with ft/s?
    That's one reason. What else does the speed of sound in a gas depend on, and is it or are they different for CO2 compared to air?
  5. Mar 31, 2010 #4
    How would you convert: 213.36 m/s into ft/s?

    Thanks for the tip!
    The speed of a gas also depends on its temperature. (Velocity increases with temperature. Temperature also affects density οƒ the higher the temp, the lower the density.) Therefore, the velocity of carbon dioxide would differ from air b/c of differences in temperatures based on the kinetic energy of molecules in the air and CO2.
  6. Mar 31, 2010 #5
    [To convert 213.23 m/s to ft/s we would get: (213.36 m/s)( 3.2808399)= 700 ft/s]

  7. Mar 31, 2010 #6
    Yes you really didn't need to do that since 2*350 = 700
  8. Mar 31, 2010 #7
    So i can leave it in m/s? Where did the 350 come from?
  9. Mar 31, 2010 #8
    You should know you calculated it yourself in your first post.

    Velocity =2ft*350HZ = 700 ft/s

    Hz is defined as s-1 "per second"
  10. Apr 1, 2010 #9
    gosh-sometimes you miss the obvious staring at you. thanks!
  11. Apr 1, 2010 #10
    Assume the carbon dioxide is the same temperature as air, because you're not told otherwise.

    Consider that air is mostly N2.

    For a given amount of kinetic energy (temperature), how does the velocity of a nitrogen molecule compare to that of a carbon dioxide molecule?
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