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# Needing help with this physics question I got wrong?

At a distance of 12m from a sound source the sound intensity is found to be 0.1W/m^2. What is the sound intensity at a distance 36m from the source?

A. 0.011 W/m^2

B. 0.1 W/m^2

C. 0.3 W/m^2

D. 0.033 W/m^2

After making the assumption to calculate and use the same density I got for 12m, I was apparently wrong to do so, so I found that the answer is not D. I am stumped on what it could be.

### 1 Answer

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- AmyLv 73 weeks ago
Think of the location of the sound as a sphere expanding over time, centered at the source.

Whatever quantity of sound was created, it stays constant but is spread over the increasing area of the sphere. Area is 2-dimensional. When the radius triples, the area is multiplied by 9; there is only 1/9 as much sound per unit of area.

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