Question

Acommuter train passes a passenger platform at a constant speed of 43.1 m/s. The train horn is sounded at its characteristic frequency of 322 Hz.

(a) What overall change in frequency is detected by a person on the platform as the train moves from approaching to receding? (Indicate whether the frequency increases of decreases with the sign of your answer.)

(b) What wavelength is detected by a person on the platform as the train approaches?

Answer 1

Solution :- Given data

V is Speeed of sound = 343m/s

vs is speed of source = 43.1 m/s

When Train is approaching

frequncy heard fL = fs*(V)/(V-Vs)

fL = frequency ehard by the listener

so

frequency while approaching = 322 * (343)/(343-43.1)

fapp = 368.276 HZ

frequency while receeding is

Freceed = fs *(V)/(V+Vs)

Frec = 322 * (343)/(343+39.8)

Frec= 286.055

change of Frequency = 368.276 -286.055= 82.221 Hz

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part B :

Wavelength L = V/fapp

L = 343/368.276

wavelengt = 0.9313meters