$A$ whistle revolves in a circle with an angular speed of $20 \; rad/s$ using a string of length $50 \; cm.$ If the frequency of sound from the whistle is $385 \; Hz,$ then what is the minimum frequency heard by an observer,who is far away from the centre in the same plane? $(v = 340 \; m/s)$

An observer moves towards a stationary source of sound,with a speed of one-fifth of the speed of sound. The apparent increase in the frequency heard by the observer is (in $\%$)

The engine of a train moving with speed $10\,ms^{-1}$ towards a platform sounds a whistle at frequency $400\,Hz$. The frequency heard by a passenger inside the train is $........\,Hz$ (neglect air speed. Speed of sound in air $330\,ms^{-1}$). (in $,Hz$)

$A$ train,standing in a station-yard,blows a whistle of frequency $400\; Hz$ in still air. The wind starts blowing in the direction from the yard to the station with a speed of $10\; m s^{-1}$. What are the frequency,wavelength,and speed of sound for an observer standing on the station's platform? Is the situation exactly identical to the case when the air is still and the observer runs towards the yard at a speed of $10\; m s^{-1}$? The speed of sound in still air can be taken as $340\; m s^{-1}$.

An observer moves towards a stationary source of sound with a speed $\frac{1}{5}$th that of sound. The frequency of the sound emitted by the source is $f$. The apparent frequency recorded by the observer is

The apparent frequency of a note,when a listener moves towards a stationary source with a velocity of $40 \ m/s$,is $200 \ Hz$. When the listener moves away from the same source with the same speed,the apparent frequency of the same note is $160 \ Hz$. The velocity of sound in air is (in $m/s$):