A burglar alarm at a business gives off a fundamental tone of 500 Hz and an appr
ID: 1634167 • Letter: A
Question
A burglar alarm at a business gives off a fundamental tone of 500 Hz and an approaching police car is travelling at a steady speed of 40 m/s. The temperature is 295.0 degree K. Assume still air. V_ = (331 + 0.6T) m/s. Where T_ = The temperature in degrees Celsius. What is the speed of sound in air at this temperature? [Watch your units!] a. 330 m/s b. 332 m/s c. 344 m/s d. 499 m/s e. 555 m/s As the police car approaches the crime scene at 40 m/s, what frequency of the burglar alarm does the responding police officer hear? a. 472 Hz b. 500 Hz c. 529 Hz d. 558 Hz e. 566 Hz What is the wavelength of the sound wave that reaches the police car? a. 0.53 meters b. 0.66 meters c. 0.69 meters d. 0.72 meters c. 0.76 meters If the police car siren sounds at the same source frequency as the alarm, what frequency will the burglar hear the approaching police siren at? a. 472 Hz b. 500 Hz c. 529 Hz d. 558 Hz e. 566 HzExplanation / Answer
Frequecy of bluglar alarm=500 Hz
Velocity of police car, Vl=40 m/s
Velocity of sound in air, Vs=(331+0.6Tc) m/s
1.
At given temperature velocity of sound in air,
Vs=(331+0.6*22))=344.2 m/s
Hence answer c is correct.
2.
As apparent frequency of alarm
f'=f((V+Vl)/V)=500[(40+344)/344]= 558.139 = 558 Hz.
The correct option is d.
3.
As wavelength = velocity/frequency = 344/500 = 0.688 meter.
The correct option is c.
4
Again
As apparent frequency of siren
f'=f(V/(V-Vl))=500[(344)/(344-40)]= 565.789 = 566 Hz.
The correct option is e.
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