A policemen buzz a whistle of frequency $400\ Hz$. A car driver is approaching the policemen. The speed of car is $54\  kmh^{-1}$. The change in frequency experienced by the driver, when driver approaches the policemen and after he crosses the policemen, is ... $Hz$ [Velocity of sound is $350\  ms^{-1}$]
  • A$42.8$
  • B$34.2$
  • C$38.6$
  • D$27.6$
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