Q. 165.0( 1 Vote )

# A train, standing in a station yard, blows a whistle of frequency 400 Hz in still air. The wind starts blowing in the direction from the yard to the station with a speed of 10m/s. Given that the speed of sound in still air is 340m/s,A. The frequency of sound as heard by an observer standing on the platform is 400Hz.B. The speed of sound for the observer standing on the platform is 350m/s.C. The frequency of sound as heard by the observer standing on the platform will increase.D. The frequency of sound as heard by the observer standing on the platform will decrease.

There no relative motion between the train and the observer, so the frequency heard by the observer is same as the frequency produced by the train.

The wind is blowing at a speed of 10m\sec in the direction in which sound wave is travelling. So, net speed of sound wave is = (350+10) m\sec = 350 m\sec.

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