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Asked by sarveshvibrantacademy | 21 Mar, 2019, 10:58: AM
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when detector is moving towards source , frquency n detected by detector is given by
 
n = no [ 1 + ( vo / v ) ]     ...............................(1)
 
where no is the frequency of sound emitted by source, vo is speed of detector and v is speed of sound.
 
since the detector is freely falling, its velocity is  vo = g×t at every t seconds starting from t=0.
 
by substituting for vo in eqn.(1), we get  n = n0 + (no g / v ) t   .................(2)
 
In the eqn.(2) that relates the frequency and time linearly,  we get the slope   (no g / v ).
 
From the given graph we have slope 1000/30  or  100/3
 
hence (no g / v ) = 100/3   or   v  = (3/100)×1000×10 = 300 m/s
Answered by Thiyagarajan K | 21 Mar, 2019, 12:32: PM

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