(adsbygoogle = window.adsbygoogle || []).push({}); [SOLVED] Sound Intensity Please help!!!

1. The problem statement, all variables and given/known data

The sound intensity level 5.0m from a point source is 95 dB. At what distance will it be 75 dB?

2. Relevant equations

dB = 10log(I/Io)

I = P/4*pi*r^2

3. The attempt at a solution

I honestly don't know what to do with this problem. I started out by plugging 5.0m and 95 dB into the equation >>

dB = 10log((P/4*pi*r^2)/Io)

>> 95 = 10log((P/4*pi*25)/1*10^-12)

>> 95 =10log(P/4*pi*25)-10log(1*10^-12)

>> 95 + 10log(1*10^-12) = 10log(P/4*pi*25)

>> -25 = 10log(P)-10log(4*pi*25)

>> -25+10log(4*pi*25) = 10log(P)

>> -.0307 = 10log(P)

>> -.00307 = log(P)

>> P = 10^-.00307

After that, I used the P that I found in the equation >>

75 = 10log((10^-.00307/4*pi*r^2)/1*10^-12)

>> 75 + 10log(1*10^-12)=10log(10^-.00307/4*pi*r^2)

>> -45 = 10log(10^-.00307)-10log(4*pi*r^2)

>> -44.95 =-10log(4*pi)+10log(r^2)

>> -33.96 = 10log(r^2)

>> -3.39 = log(r^2)

>> r^2 = 10^-3.39

>> r = .0200

This doesn't make any sense at all, but I don't know what I'm doing wrong. Our physics teacher didn't teach us the lesson on this. He just gave us a bunch of formulas and told us to figure it out. Am I using the wrong formulas, or am I making a stupid math error? Please help!!!

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# Homework Help: Sound Intensity Please help

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