question_answer 21)

                A train, standing in a stationyard, blows a whistle of frequency 400 Hz in still air. The wind starts  blowing in the direction from the yard to the station at a speed of 10 . What are the frequency, wavelength, and speed of sound for an observer standing on the station's platform ? Is the situation       exactly identical to the case when the air is still and the observer runs towards the yard at a speed of  10  ? The speed of sound in still air can be taken as 340 .  

Answer:

Here, v = 400 Hz, As, the wind is blowing in the direction of sound, therefore, effective speed of sound      As, the source and listener, both are at rest, therefore, frequency remains unchanged, i.e., v = 400 Hz wavelength,   (b) When air is still,   Speed of observer, As, observer moves towards the source,   As, source is at rest, wavelength does not change, i.e., Also, speed of sound The situations in the two cases are entirely different.