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Question
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 10 m/s. Given that the speed of sound in still air is 340 m/s ______.
- the frequency of sound as heard by an observer standing on the platform is 400 Hz.
- the speed of sound for the observer standing on the platform is 350 m/s.
- the frequency of sound as heard by the observer standing on the platform will increase.
- the frequency of sound as heard by the observer standing on the platform will decrease.
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Solution
a and b
Explanation:
Given, v0 = 400 Hz, v = 340 m/s
Speed of wind, vw = 10 m/s
a. As both source and observer are stationary. hence frequency observed will be the same as natural frequency v0 = 400 Hz
b. The speed of sound v = v + vw = 340 + 10 = 350 m/s
c. and d. There will be no effect on frequency because there is no relative motion between source and observer hence c. and d. are incorrect.
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