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The longitudinal displacement of sound wave

  1. Dec 17, 2016 #1
    1. The problem statement, all variables and given/known data

    The longitudinal displacement of a mass element in a medium as a sound wave passes through it is given by s = sm cos (kxωt). Consider a sound wave of frequency 330 Hz and wavelength 0.95 m. If sm= 16 µm, what is the displacement of an element of air located at x = 1.1 m at time t = 0.12 s?
    2. Relevant equations
    k=2π/λ
    ω=2πƒ
    ƒ≡ frequency
    ω≡ angular frequency
    λ≡ wavelength
    k≡ angular wave number

    3. The attempt at a solution
    substitute the values of λ and f in k and ω to get k=6.6138 m^-1 and ω=2073.45
    ∴ s= 16 cos ( 6.6138*1.1-2073.45*0.12)=-7.625 INCORRECT
    Where I made mistake?
     
  2. jcsd
  3. Dec 17, 2016 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    The argument of the cosine function is in what units? Radians or degrees?
     
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