How intensity and amplitude depends from a distance r

[AndreAo]

Homework Statement

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.

Homework Equations

Intensity = Power/Area

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 $$\propto$$ r². Then I $$\propto$$ r⁻². Is the reasoning right?

 

[kfnucjk]

what is this？I totally confused

 

[gneill]

A relatively ancient (yr 2009) post that had no replies. Likely no-one at the time could interpret the problem statement cogently either. Best to just move on and let it rest.