Question

A police siren has a frequency of 340.0 Hz when the car is stationary and the temperature is 20°C. The police car at point S moves to the right with a speed of 22.0 m/s.
a. What frequency does observer A hear?
b. What frequency does observer B hear?
c. Suppose observer A is moving toward the stationary police car. What is the speed of observer A if the frequency heard is 369 Hz?

Answer 1

Answer:

a) 361.7 Hz

b) 318.1 Hz

c) 29.3 m/s

Explanation:

a) Speed of sound in 20 degrees celcius is 343 m/s.

Use v=wavelength*frequency to find wavelength.

343=wavelength*340

wavelegth=1.009 meters

Relative speed of waves to observer A = 343+22 = 365 m/s

Plug it back in.

365=1.009*F

F=361.7 Hz

b) Relative speed of waves to observer B = 343-22 = 321 m/s

Plug it back in.

321=1.009*F

F=318.1 Hz

c) STATIONARY CAR, so 369Hz=v/1.009. v=372.3, 372.3-343=29.3m/s!