$A$ source of sound whose frequency is $1000 \text{ Hz}$ is moving with a speed of $33 \text{ m/s}$. The waves reflected by a fixed obstacle are registered by a receiver that moves together with the source. If the speed of the sound waves is $330 \text{ m/s}$, then the frequency registered by the receiver is: (in $\text{ kHz}$)

An observer moves towards a stationary source of sound of frequency $n$. The apparent frequency heard by him is $2n$. If the velocity of sound in air is $332 \, m/s$,then the velocity of the observer is .... $m/s$.

When a source of sound moves towards a stationary observer,the apparent frequency heard by him

$A$ stationary tuning fork is in resonance with an air column in a pipe. If the tuning fork is moved with a speed of $2 \ m/s$ in front of the open end of the pipe and parallel to it,the length of the pipe should be changed for the resonance to occur with the moving tuning fork. If the speed of sound in air is $320 \ m/s$,the smallest value of the percentage change required in the length of the pipe is. . . . . .

$A$ whistle of frequency $540 Hz$ rotates in a horizontal circle of radius $2 m$ at an angular speed of $15 rad/s$. What is the highest frequency heard by a listener at rest with respect to the center of the circle (in $Hz$)? (Velocity of sound in air $= 330 m/s$)

Two cars $A$ and $B$ are moving in the same direction with speeds $36 \, km/hr$ and $54 \, km/hr$ respectively. Car $B$ is ahead of $A$. If $A$ sounds a horn of frequency $1000 \, Hz$ and the speed of sound in air is $340 \, m/s$,the frequency of sound received by the driver of car $B$ is ................. $Hz$.