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Homework Help: Pressure Variation in Sound Waves

  1. Nov 16, 2014 #1
    1. The problem statement, all variables and given/known data
    Write an expression that describes the pressure variation as a function of x and t for the waves in air (0∘C) if the air molecules undergo a maximum displacement equal to the diameter of an oxygen molecule, about 3.0×10^−10m. Assume a sound-wave frequency of 55 Hz.
    Express your answer in terms of the variables x, t, and appropriate constants using two significant figures.

    2. Relevant equations
    ∆P = -∆Pmax cos(kx-wt)

    ∆Pmax= BAk = rho v^2 A K = 2pi rho v A f (where v is velocity)

    V sound in air = 331.3 m/s + 0.6t (in celcius)
    3. The attempt at a solution
    Plugging into the formulas I get: v sound in air = 331.3m/s

    so ∆Pmax = 2 pi (1.29 kg/m^3) 331.3m/s (3 x 10^-10m) 55 Hz = 4.43 x 10^-5

    k = 2pif/v = 1.04
    w = 2 pi f = 345.57

    Final Answer : ∆P = - 4.4 x 10^-5 cos(1.0x - 350t)
    I also tried with the ∆P =∆Pmax sin (kx - wt) version of the formula, and the website says both are wrong. I'm not really sure where I'm going wrong with this problem; thanks for any help!
  2. jcsd
  3. Nov 21, 2014 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
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