The pitch of a whistle of an engine appears to drop by $30 \%$ 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:

Match Column-$A$ with Column-$B$.

Column-$A$	Column-$B$
$(a)$ When source of sound and listener move towards wall.	$(i)$ Listener would hear a sound with same frequency as that of source.
$(b)$ When source of sound and listener move away from each other.	$(ii)$ Listener would hear a sound with frequency smaller than that of source.
	$(iii)$ Frequency of echo would be greater than that of source.

$A$ car moves towards a hill with speed $v_c$. It blows a horn of frequency $f$ which is heard by an observer following the car with speed $v_o$. The speed of sound in air is $v$.

The observer is moving with velocity $v_0$ towards the stationary source of sound and then after crossing moves away from the source with velocity $v_0$. Assume that the medium through which the sound waves travel is at rest. If $v$ is the velocity of sound and $n$ is the frequency emitted by the source,then the difference between apparent frequencies heard by the observer is:

$A$ stationary source is emitting sound at a fixed frequency $f_0$,which is reflected by two cars approaching the source. The difference between the frequencies of sound reflected from the cars is $1.2\%$ of $f_0$. What is the difference in the speeds of the cars (in $km/h$) to the nearest integer? The cars are moving at constant speeds much smaller than the speed of sound,which is $330 \ m/s$.

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 ..... $Hz$.