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Homework Help: How intensity and amplitude depends from a distance r

  1. Nov 8, 2009 #1
    1. The problem statement, all variables and given/known data
    A line source of sound (for instance, a noisy freight train on a straight track) emits a cylindrical expanding sound wave. Assuming that the air absorbs no energy, find how (a) the intensity I and (b) the amplitude sm of the wave depends on the perpendicular distance r from the source.

    2. Relevant equations
    Intensity = Power/Area

    3. The attempt at a solution
    I thought that the area would be something like the base of a circular cone, and the area of it base would A [tex]\propto[/tex] r². Then I [tex]\propto[/tex] r⁻². Is the reasoning right?
  2. jcsd
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