Question

An aircraft is moving away from you at half the speed of sound, which, on that day is about 340 m/s.

The jet engines make a sound that is primarily about 300 Hz. What is the apparent frequency of the jet

engines?

(A) 150 Hz

(B) 200 Hz

(C) 470 Hz

(D) 600 Hz

Answer 1

(B) 200 Hz

Step-by-step explanation:

To find the apparent frequency you use the Doppler effect for a receding source:

`f'=f((v)/(v+v_s))`

f: frequency of the source = 300Hz

v: speed of souns = 340m/s

v_s: speed of the source = v/2 = 170m/s

you replace the values of the parameters and obtain:

`f'=(300Hz)((340m/s)/(340m/s+170m/s))=200Hz`

hence, the apparent frequency is 200Hz

(B) 200 Hz