A train is approaching a signal tower at a speed of 40 m/s. The train engineer s

Question

A train is approaching a signal tower at a speed of 40 m/s. The train engineer sounds the 1000 hz whistle, while a switchman in the tower responds by sounding the 1200 hz siren. The air is still and the speed of sound is 340 m/s. What is the frequency of the train whistle tone that is heard by the switch man? A) 340/300 * 1000 hz B) 340/380 * 1000 hz C) 300/340 * 1000 hz D) 380/340 * 1000 hz E) 1000 hz A train is approaching a signal tower at a speed of 40 m/s. The train engineer sounds the 1000 hz whistle, while a switchman in the tower responds by sounding the 1200 hz siren. The air is still and the speed of sound is 340 m/s. What is the frequency of the train whistle tone that is heard by the switch man? A) 340/300 * 1000 hz B) 340/380 * 1000 hz C) 300/340 * 1000 hz D) 380/340 * 1000 hz E) 1000 hz A) 340/300 * 1000 hz B) 340/380 * 1000 hz C) 300/340 * 1000 hz D) 380/340 * 1000 hz E) 1000 hz

Explanation / Answer

Given data

vS = 40 m/s.

frequency, fS = 1000 hz

speed of sound v = 340 m/s.

Solution :-

The frequency fL that the switchman perceives is given by fL = fS*(v / (v+vS) .

Frequency = 1000* [340 / (340+40)]

Frequency = [340/380] * 1000 Hz (option B)

            = 894.73 Hz

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