A sound wave from a police siren has an intensity of 103.8 W/m2 at a certain poi

Question

A sound wave from a police siren has an intensity of 103.8 W/m2 at a certain point; a second sound wave from a nearby ambulance has an intensity level that is 12 dB greater than the police siren's sound wave at the same point. What is the intensity level of the sound wave due to the ambulance? A driver travels northbound on a highway at a speed of 30.0 m/s. A police car, traveling southbound at a speed of 39.0 m/s, approaches with its siren producing sound at a frequency of 2600 Hz. What frequency does the driver observe as the police car approaches? What frequency does the driver detect after the police car passes him? Repeat parts (a) and (b) for the case when the police car is traveling northbound, while police car overtakes after police car passes Need Help?

Explanation / Answer

A. L = 10log(103.8/Io)

12+L = 10log(I/Io)

12 = 10log(I/103.8)

I =344.62 W/m2

in dB , L = 10log(344.62/10^-12)

= 145.37 dB

B. 1. f = (343+30)/(343-39)*2600 = 1.23*2600 = 3198 Hz

2. f = (344-30)/(343+39)*2600 = 2130.36 Hz

C. f = (344-30)/(343-39)*2600 = 2685.52 Hz

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