A whistle of frequency 500 Hz tied to the end of a string of length 1.2 m revolves at 400 rev/min. A listener standing some distance away in the plane of rotation of whistle hears frequencies in the range (speed of sound = 340 m/s

(1) 436 to 586

(2) 426 to 574

(3) 426 to 584

(4) 436 to 674

(1) The linear velocity of Whistle

vS=rω=1.2×2π40060=50m/s

When Whistle approaches the listener, heard frequency will be maximum and when listener recedes away, heard frequency will be minimum

So, nmax=nvvvs=500340290=586Hz

nmin=nvv+vs=500340390=436Hz

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