$A$ source with frequency $f$ and an observer are moving towards each other with a velocity of $V/10$. The frequency heard by the observer will be ............ $f$. (The velocity of sound in air is $V \, m/s$.)

$A$ sound source $S$ is moving along a straight track with speed $v,$ and is emitting sound of frequency $v_{0}.$ An observer is standing at a finite distance,at the point $O,$ from the track. The time variation of frequency heard by the observer is best represented by (where $t_{0}$ represents the instant when the distance between the source and observer is minimum).

$A$ detector is released from rest over a source of sound of frequency $f_0 = 10^3 \, Hz$. The frequency observed by the detector at time $t$ is plotted in the graph. Given $g = 10 \, m/s^2$,find the speed of sound in air in $m/s$.

$A$ stationary source of sound $A$ is producing sound of frequency $170 \, Hz$. Another source of sound $B$ producing sound of frequency $240 \, Hz$ is moving towards the source $A$ on a straight path with a uniform speed of $20 \, ms^{-1}$. An observer between $A$ and $B$ is moving towards the source $A$ along the straight path $BA$. If the number of beats heard by the observer is zero, the speed of the observer is . . . . . . $ms^{-1}$. (Speed of sound in air $= 340 \, ms^{-1}$).

Two factories are sounding their sirens at $800 \, Hz$. $A$ man walks from one factory to the other at a speed of $2 \, m/s$. The velocity of sound is $320 \, m/s$. The number of beats heard by the person in one second will be:

Statement $-1$: Due to the motion of the listener,the frequency of the sound waves (as received by the listener) emitted by a stationary source is affected.
Statement $-2$: Due to the motion of the source,the wavelength of the sound waves (emitted by the source) as received by a stationary listener is affected.
Statement $-3$: If the receiver and the source are both moving,the observed frequency must be different from the original frequency of the source.
Treat the motion of the source or listener as always along the line joining them for all the above cases.