$A$ car sounding a horn of frequency $1000 \text{ Hz}$ passes an observer. The ratio of frequencies noted by the observer before and after the car passes is $11:9$. If the speed of sound is $V$,what is the speed of the car?

$A$ source of sound emits sound waves at frequency $f_0$. It is moving towards an observer with fixed speed $v_s$ ($v_s < v$,where $v$ is the speed of sound in air). If the observer were to move towards the source with speed $v_0$,the variation of the frequency $f$ heard by the observer as $v_0$ is changed is given by one of the following two graphs ($A$ and $B$). The variation of $f$ with $v_0$ is given correctly by:

$A$ person driving a car at a constant speed of $15\,m/s$ is approaching a vertical wall. The person notices a change of $40\,Hz$ in the frequency of his car's horn upon reflection from the wall. The frequency of the horn is ............ $Hz$. (Given: Speed of sound: $330\,m/s$)

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

$A$ car moving towards a wall at a velocity of $72 \,km/hr$ sounds a horn of frequency $124 \,vib/sec$. What frequency will the driver hear? (Speed of sound in air = $330 \,ms^{-1}$)

$A$ source of sound $S$ of frequency $500 \ Hz$ situated between a stationary observer $O$ and a wall $W$,moves towards the wall with a speed of $2 \ m/s$. If the velocity of sound is $332 \ m/s$,then the number of beats per second heard by the observer is (approximately)