$A$ policeman blows a whistle of frequency $400 \ Hz$. $A$ car driver is approaching the policeman. The speed of the car is $54 \ km/h$. The change in frequency experienced by the driver,when the driver approaches the policeman and after he crosses the policeman,is ... $Hz$ [Velocity of sound is $350 \ m/s$]

$A$ source of sound emits a sound wave of frequency '$f$' and moves towards an observer with a velocity $\frac{V}{3}$,where $V$ is the velocity of sound. If the observer moves away from the source with a velocity $\frac{V}{5}$,the apparent frequency heard by him will be:

The difference between the apparent frequency of a source of sound as perceived by an observer during its approach and recession is $2\%$ of the natural frequency of the source. If the velocity of sound in air is $300 \, m/s$,the velocity of the source is ... $m/s$ (Given that velocity of source < velocity of sound).

$A$ source of sound $S$ emitting waves of frequency $100 \, Hz$ and an observer $O$ are located at some distance from each other. The source is moving with a speed of $19.4 \, m s^{-1}$ at an angle of $60^{\circ}$ with the source-observer line as shown in the figure. The observer is at rest. The apparent frequency observed by the observer is .... $Hz$ (velocity of sound in air $330 \, m s^{-1}$).

An observer is standing $500 \,m$ away from a vertical hill. Starting between the observer and the hill, a police van sounding a siren of frequency $1000 \,Hz$ moves towards the hill with a uniform speed. If the frequency of the sound heard directly from the siren is $970 \,Hz$, the frequency of the sound heard after reflection from the hill (in $Hz$) is about, (velocity of sound $= 330 \,m/s$):

$A$ table is revolving on its axis at $5$ revolutions per second. $A$ sound source of frequency $1000 \text{ Hz}$ is fixed on the table at $70 \text{ cm}$ from the axis. The minimum frequency heard by a listener standing at a distance from the table will be .... $\text{ Hz}$ (speed of sound $= 352 \text{ m/s}$)