1. The problem statement, all variables and given/known data A rock group is playing in a club. Sound emerging outdoors from an open door spreads uniformly in all directions. If the decibel level is 70 dB at a dis- tance of1.0 m from the door,at what distance is the music just barely audible to a person with a normal threshold ofhearing? Disregard absorption. Given: dB1 = 70 dB r1 = 1.0 m Unknowns: I1 = ? r2 = ? Io = 10^-12 W/m^2 dB1 is the decibel level at a distance of 1m from the door. r1 is distance from the door. I1 is intensity at a distance 1m (r1) from the door. Io is threshold of hearing, at a distance of r2 (unknown) from the door. 2. Relevant equations dB = 10 log(I/Io) I = P/A = P/4πr^2 3. The attempt at a solution db = 10 log(I/Io) 70 = 10 log(I/Io) 7log10 = log(I/Io) 10^7 = I/Io 10^-12 * 10^7 = I I1 = 10^-5 W/m^2 -> Intensity 1 I1 = P/A 10^-5 = P/(4π) P = 1.3 x 10^-4 W Now I used the same equation to find r of threshold of hearing: Io = P/A 10^-12 = (1.3 x 10^-4)/(4πr^2) r = sqrt([1.3x10^-4]/[10^-12x4π]) = 3216 m This is what I got for r, but it just doesn't seem reasonable. Is this the correct answer? Have I done something wrong? Thank you, and please do tell if my work is incomprehensible.