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?