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An interstate highway has been built though a poor neighborhood in a city. In the afternoon, the sound level in a rented room is 114.0 dB as 172 cars pass outside the window every minute. Late at night, the traffic flow is only 7 cars per minute.
(b) What is the sound intensity at night? (c) What is the average late-night sound level?

86 cars (half of them) is 3 db down
43 cars will be down another 3 db
22 cars (appx) will be down another 3 db
11 cars will be down another 3 db

I estimating, 7 cars will be 114-14 db.

Doing the math:
Intnsity=10log(power/E-12)
112=10log(EachCar*172/E-12)
11.2=log( )
taking theantilog of each side.

E11.2=Each car*172/E-12
E-.8=each car*172

each car= .158/172

sound intensity at night:
Inight=10log(7*.158/172E-12)=98db

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