A jet airplane has an intensity of 92.4 W/ m2 when heard at a distance of 21.2 m. What is the maximum sound intensity heard by a person on the ground when the airplane is 10700 m overhead?
Assume that sound propagation is isotropic (uniform in direction) although it might not be, for jet engines.
10,700 m is a typical cruising altitude (35,000 feet), by the way.
According to the inverse square law, the intensity at 10,700 m will be
92.4*(21.2/10,700)^2 = 3.6*10^-4 W/m^2
That is a sound level of about 85dB