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 0.11w/m2.

an intensity of 1.0w/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?

5 m

Explanation:

We have the following data:

is the intensity of the sound at 7.5 m from the source

is the distance at which the intensity was measured

is the intensity of the sound at from the source

We have to find

Since the object is radiating the signal uniformly in all directions, we can use the Inverse Square Law for Intensity:

Isolating :

This is the distance at which the intensity is the "threshold of pain"

Now, we have to substract this value to to find how much closer to the source can we move:

a.   mass number from atomic number

+15-35=-20

going in opposite directions