Threshold of Pain. You are investigating the report of a UFO landing in an isolated portion of New Mexico, and you 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 W/m2. An intensity of 1.0 W/m2 is often used as the “threshold of pain.” How much closer to the source can you move before the sound intensity reaches this threshold?
Solution 26E Step 1: Initial Intensity I = 0.11 W/m 2 1 Final Intensity I = 1.0 W/m 2 2 Initial Radius R =17.5 m Final Radius R = 2