A train moves towards a stationary observer with speed 34 m/s. The train sounds a whistle and its frequency registered by the observer is f1. If the train’s speed is reduced to 17 m/s, the frequency registered is f2. If the speed of sound is 340 m/s then the ratio f1/f2 is 

(1) 18/19

(2) 1/2

(3) 2

(4) 19/18

(4) By using n'=n  vvvS

f1=nvvvS=n34034034=340306n

and f2=n34034017=n340323

f1f2=323306=1918

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