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Sound Intensity and Threshold of pain

You are investigating the report of a UFO landing in an isolated portion of New Mexico, and encounter a strange object that is radiating sound waves uniformly in all directions. Assume that the sound comes from a point source and that you can ignore reflections. You are slowly walking toward the source. When you are 7.5 m from it, you measure its intensity to be 0.11;{rm W}/{rm m}^{2}.

a). An intensity of 1.0;{rm W}/{rm m}^{2} is often used as the "threshold of pain". How much closer to the source can you move before the sound intensity reaches this threshold?
Express your answer using two significant figures.

Solution Preview

I1 = 0.11 W/m^2, I2 = 1 W/m^2, r1 = 7.5 m

To find: r2

The sound intensity from a ...

Solution Summary

The sound intensity from a point source varies inversely as the square of the distance from it.

I1/I2 = (r2/r1)^2 ...