An engine sounding a whistle of frequency $2000 \,Hz$ is receding from a stationary observer at $72 \,km/h$. What is the apparent frequency heard by the observer (in $\,Hz$)? The velocity of sound in air is $340 \,m/s$.

Consider two tuning forks with natural frequency $250 \,Hz$. One is moving away and another is moving towards a stationary observer at the same speed. If the observer hears beats of frequency $5 \,Hz$, then the speed of the tuning fork is: (Given, speed of sound wave is $350 \,m/s$.) (in $\,m/s$)

$A$ source and a listener are both moving towards each other with a speed of $\frac{V}{10}$ (where $V$ is the speed of sound). If the frequency of the sound note emitted by the source is $n$,then the frequency heard by the listener would be nearly:

An audio transmitter $(T)$ and a receiver $(R)$ are hung vertically from two identical massless strings of length $8 \ m$ with their pivots well separated along the $X$ axis. They are pulled from the equilibrium position in opposite directions along the $X$ axis by a small angular amplitude $\theta_0 = \cos^{-1}(0.9)$ and released simultaneously. If the natural frequency of the transmitter is $660 \ Hz$ and the speed of sound in air is $330 \ m/s$,the maximum variation in the frequency (in $Hz$) as measured by the receiver (Take the acceleration due to gravity $g = 10 \ m/s^2$) is:

$A$ whistle giving out $450 Hz$ approaches a stationary observer at a speed of $33 m/s$. The frequency heard by the observer in $Hz$ is (Take speed of sound $v = 330 m/s$)

An observer starts moving with uniform acceleration $a$ toward a stationary sound source emitting a whistle of frequency $n$. As the observer approaches the source,the apparent frequency $n'$ heard by the observer varies with time $t$ as: