The source producing sound and an observer are both moving along the direction of propagation of sound waves. If the respective velocities of sound,source,and an observer are $v$,$v_s$,and $v_o$,then the apparent frequency heard by the observer will be ($n =$ frequency of sound).

$A$ 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 $330 \ m/s$.

$A$ vehicle with a horn of frequency $n$ is moving with a velocity of $30\, m/s$ in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency $n + n_1$. Then (if the sound velocity in air is $300\, m/s$):

The frequency of a whistle of an engine is $600 \, Hz$ and it is moving with a speed of $30 \, m/s$ towards a stationary observer. The apparent frequency heard by the observer will be .... $Hz$ (velocity of sound $= 330 \, m/s$).

$A$ sound source is moving towards a stationary observer with $\frac{1}{10}$th the speed of sound. The ratio of apparent to real frequency is

$A$ siren placed at a railway platform is emitting a sound of frequency $5 \text{ kHz}$. $A$ passenger sitting in a moving train $A$ records the frequency of the siren as $5.5 \text{ kHz}$. During his return journey by train $B$,he records the frequency of the siren as $6 \text{ kHz}$. The ratio of the speed of train $B$ to that of train $A$ is