A Man Facing A Wall Holds A Tuning Fork Of Frequency 256 Hz Between Himself And A Vertical Wall. He Moves The Tuning Fork Towards The Wall With A Velocity 1/100 Of The Velocity Of Sound. The Number Of Beats Heard Per Minute Would Be:

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A man facing a wall holds a tuning fork of frequency 256 Hz between himself and a vertical wall. He moves the tuning fork towards the wall with a velocity 1/100 of the velocity of sound. The number of beats heard per minute would be:


Correct option is



The tuning fork is a source moving away from the observer, while the sound reflected from the wall is moving towards the observer. Thus, we have two sources of the same frequency, one moving away and the other moving towards the observer with the same velocity. If v is the velocity of sound, vs the velocity of the source, the apparent frequency difference is:  


 we get number of beats = frequency difference = 5/sec = 300 per minute.



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In a good tuning fork: