$A$ police car horn emits a sound at a frequency $240 \text{ Hz}$ when the car is at rest. If the speed of sound is $330 \text{ m/s}$,the frequency heard by an observer who is approaching the car at a speed of $11 \text{ m/s}$ is ... $\text{ Hz}$.

$A$ 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 ..... $Hz$.

Two cars are moving on two perpendicular roads towards a crossing with uniform speeds of $72\; km/hr$ and $36\; km/hr$. If the first car blows a horn of frequency $280\; Hz$,then the frequency of the horn heard by the driver of the second car when the line joining the cars makes a $45^o$ angle with the roads will be .... $Hz$.

$A$ motor-cyclist moving towards a huge cliff with a speed of $18 \ kmh^{-1}$,blows a horn of source frequency $325 \ Hz$. If the speed of the sound in air is $330 \ ms^{-1}$,the number of beats heard by him is

$A$ whistle emitting a loud sound of frequency $540 \,Hz$ is whirled in a horizontal circle of radius $2 \,m$ at a constant angular speed of $15 \,rad/s$. The speed of sound is $330 \,m/s$. The ratio of the highest to the lowest frequency heard by a listener standing at rest at a large distance from the centre of the circle is

$A$ $SONAR$ 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 $1450 \; m/s$.