A whistle emitting a sound of frequency 440 Hz is said to a string of 1 . 5 m length and rotated with an angular velocity of20 rad,/s in horizontal plane. Then the range of frequencies heard by an observer stationed at a large distance from the whistle will be (v = 330 m/s)

see figThe observer will hear the frequency (maximum) when the source is in position D because source is moving  towards observer almost along the line of sight. So,nmax=VV−Vsn=330330−1⋅5×20440 =330300×440=484HzThe observer will hear the frequency (minimum) when the source is in position I because the source is moving away from the observer. So,nmin=vv+vs×n =330330+1⋅5×20×440 =330360×440=403⋅3Hz