A train sounds its horn as it approaches an intersection. The horn can just be heard at a level of 52 dB by an observer 10 kilometer away.
(a) Obtain the average power generated by the horn?
_________W
(b) Find what intensity level of the horn's sound is observed by someone waiting at an intersection 42 meter from the train? Treat the horn as a point source and ignore any absorption of sound by the air.
_________dB