A tornado warning siren at the top of a tall pole radiates sound waves uniformly
in all directions. At a distance of 10 [m], the intensity of sound is 0.49 [W/m2] .
What is the intensity at a distance of 70 [m] from the siren?
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Answers & Comments
I think that in this question you are expected to assume that the inverse square law applies in a very simplistic way.
if p = power density , r = distance, k = constant, then
p = k/r^2
or p1 r1^2 = p2 r2^2
using p1 = 0.49, r1 = 10m, r2 = 70, we can write -
p2 = (p1 r1^2)/r2^2 = 0.01W/m^2
But I would like to comment that this is completely unrealistic. In the real world the sound will be reflected off the ground any all nearby objects, and the inverse square law will not be obeyed at all. The inverse sqare law only applies when the wavefront expands into empty space which is completely free of obstacles. I hope that your teacher is firmly grounded in the real world lol.