A train has just complicated a $U-$curve in a track which is a semicircle. The engine is at the forward end of the semi circular part of the track while the last carriage is at the rear end of the semicircular track. The driver blows a whistle of frequency $200 Hz.$ Velocity of sound is $340 m/sec$. Then the apparent frequency as observed by a passenger in the middle of a train when the speed of the train is $30 m/sec$ is ... $Hz$
Diffcult
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