$A$ source of sound is travelling towards a stationary observer. The frequency of sound heard by the observer is three times the original frequency. If the velocity of sound is $v \ m/s$,the speed of the source will be:

$A$ car sounding its horn at $480\,Hz$ moves towards a high wall at a speed of $20\,m/s$. If the speed of sound is $340\,m/s,$ the frequency of the reflected sound heard by the passenger sitting in the car will be the nearest to ..... $Hz$.

$A$ man standing on a platform observes that the frequency of the sound of a whistle emitted by a train drops by $140 \, Hz$. If the velocity of sound in air is $330 \, m/s$ and the speed of the train is $70 \, m/s$,the frequency of the whistle is .......... $Hz$.

$A$ $SONAR$ system fixed in a submarine operates at a frequency of $40.0 \; kHz$. An enemy submarine moves towards the $SONAR$ with a speed of $360 \; km/h$. What is the frequency (in $kHz$) of sound reflected by the submarine (in $; kHz$)? Take the speed of sound in water to be $1450 \; m/s$.

$A$ source of sound of frequency $256 \ Hz$ is moving rapidly towards a wall with a velocity of $5 \ m/s$. The speed of sound is $330 \ m/s$. If the observer is between the wall and the source,then the number of beats per second heard will be .... $Hz$.

$A$ source of sound is moving towards a stationary observer with velocity $V_s$ and then moves away with velocity $V_s$. 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 the apparent frequencies heard by the observer is: