A commuter train passes a passenger platform at a constant speed of 39.7 m/s. Th

Question

A commuter train passes a passenger platform at a constant speed of 39.7 m/s. The train horn is sounded at its characteristic frequency of 320 Hz.

A commuter train passes a passenger platform at a constant speed of 39.7 m/s. The train horn is sounded at its characteristic frequency of 320 Hz. 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.) Your response differs from the correct answer by more than 10%. Double check your calculations. Hz What wavelength is detected by a person on the platform as the train approaches?

Explanation / Answer

a) (343 + 39.7) = 382.7 m/sec. apparent sound speed approaching

and (343 - 39.7) = 303.3m/sec. apparent sound speed when giong away.

(382.7/343) x 320Hz = 357.038 Hz approaching, and (303.3/343) x 320Hz = 282.9621Hz. receding.

(357.038 - 282.9621) = 74.076 Hz total frequency shift.

b) Wavelength = velocity/frequency, the apparent frequency as the train approaches is 357.038 Hz.

(343/357.038) = .9607m

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