The difference between the apparent frequency of a source of sound as perceived by an observer during its approach and recession is 2% of the natural frequency of the source. If the velocity of sound in air is 300 m/sec, the velocity of the source is (It is given that velocity of source << velocity of sound) 

(1) 6 m/sec

(2) 3 m/sec

(3) 1.5 m/sec

(4) 12 m/sec

(2) When the source approaches the observer

Apparent frequency n'=vvvs.n=n11vsv

= n1vsv1=n1+vsv

(Neglecting higher powers because vS << v)

When the source recedes the observed apparent frequency n''=n1vsv

Given n'n''=2100n,  v=300 m/sec

2100n=n1+vsvn1vsv=n2vsv

2100=2vsvvs=v100=300100=3 m/sec

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