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June 10th, 2007, 07:11 AM   #1
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Dont know how to start

A loudspeaker is placed between two observers who are 120 m apart, along the line connecting them. If one observer records a sound level of 60.0 dB and the other records a sound level of 90 dB, how far is the speaker from each observer?


3.7,116.3

4.3,115.7

6.2,113.8

8.6,111.4
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July 30th, 2007, 05:58 AM   #2
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Re: Dont know how to start

The observer finds the 90dB speaker 1000 times as powerful as the 60dB speaker (10 times for each 10 dB), and power observed is inversely proportional to the square of the distance from the speaker. Hence you want to find distances in a ratio which is the square root of 1000. The first choice (3.7, 116.3) fits the bill (assuming those figures have been rounded to one decimal place).
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