An observer moves towards a stationary source of sound with a velocity one-fifth of the velocity of sound. The percentage change in the apparent frequency is ..... $\%$

$A$ source and an observer approach each other with the same velocity $50 \, m/s$. If the apparent frequency is $435 \, s^{-1}$,then the real frequency is .... $s^{-1}$ (Take speed of sound $v = 332 \, m/s$)

Two sources of sound $S_1$ and $S_2$ produce sound waves of same frequency $660\, Hz$. $A$ listener is moving from source $S_1$ towards $S_2$ with a constant speed $u\, m/s$ and he hears $10\, \text{beats/s}$. The velocity of sound is $330\, m/s$. Then, $u$ equals ... $m/s$.

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:

Obtain the equation of frequency observed by a moving observer and a stationary source.

$A$ 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 $330 \ m/s$.