Question

a train sounds its horn as it approaches an intersection. The horn can just be heard at a level of 40dB by an observer 10 km away.

a) what is the average power generated by the horn?

b) what intensity level of the horn's sound is observed by someone waiting at an intersection 58m from the train? Treat the horn as a point source and neglect any absorption of sound by the air.

Answer 1

a Avenage Power by the horno generated va Sound level B B = 10 log los de Io = 1 x 10-12 w W m2 B = 40 dB & Intensity of sound at 10 km from horn is, Blio ㅂ 4 Io 10 = (1 x 10-12) 10 -8 1 x 10 Wim? 6. I

wave a 7 Intensity of Spherical produced by Point source with the Power Emitted, P H 5 4792 Average T powes , P = utre? = 4T (10 x103)? (IXIÓ -६, o p = 12.56 W

b Intensity level 6 the at 4 = 58m intensity is I s Р 4t ei? = 12.56 4T (58) 8. I a -4 2.97 x 10 W/m² = Intensity level, B B = 10 log (1110) (2.92*10-4) = 10 log 10-12 B = 84 dB