$A$ source at rest emits sound waves of frequency $102 \ Hz$. Two observers are moving away from the source of sound in opposite directions, each with a speed of $10 \%$ of the speed of sound. The ratio of the frequencies of sound heard by the observers is

Two vehicles,each moving with speed $u$ on the same horizontal straight road,are approaching each other. Wind blows along the road with velocity $w$. One of these vehicles blows a whistle of frequency $f_1$. An observer in the other vehicle hears the frequency of the whistle to be $f_2$. The speed of sound in still air is $V$. The correct statement$(s)$ is (are) :
$(A)$ If the wind blows from the observer to the source,$f_2 > f_1$.
$(B)$ If the wind blows from the source to the observer,$f_2 > f_1$.
$(C)$ If the wind blows from the observer to the source,$f_2 < f_1$.
$(D)$ If the wind blows from the source to the observer,$f_2 < f_1$.

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 $,Hz$)

The frequency of a car horn changes from $400\, Hz$ to $500\, Hz$ as the car approaches a vertical wall. If the speed of sound is $330\, m/s$,then the speed of the car is $.....\, km/h$.

The pitch of the whistle of an engine appears to drop by $20 \%$ of its original value when it passes a stationary observer. If the speed of sound in air is $350 \ m/s$,then the speed of the engine in $m/s$ is:

The frequency changes by $10\%$ as a sound source approaches a stationary observer with constant speed $v_s$. What would be the percentage change in frequency as the source recedes from the observer with the same speed? (Given that $v_s < v$,where $v$ is the speed of sound in air)