$A$ source of sound of frequency $450 \text{ cycles/sec}$ is moving towards a stationary observer with $34 \text{ m/sec}$ speed. If the speed of sound is $340 \text{ m/sec}$,then the apparent frequency will be ..... $\text{cycles/sec}$.

An observer and a source emitting sound of frequency $120 \,Hz$ are on the $X$-axis. The observer is stationary while the source of sound is in motion given by the equation $x=3 \sin \omega t$ (where $x$ is in metres and $t$ is in seconds). If the difference between the maximum and minimum frequencies of the sound observed by the observer is $22 \,Hz$,then the value of $\omega$ is (speed of sound in air $=330 \,ms^{-1}$):

When a train is approaching a stationary observer,the apparent frequency of the whistle of the train is $n_1$,and when the train is moving away from the observer,the apparent frequency is $n_2$. The frequency of the whistle noticed by the observer when he moves with the train is . . . . . . .

$A$ drone fitted with a siren is flying directly away from the drone operator and towards a distant building at a speed of $15 \,m/s$. The siren produces a sound of frequency $780 \,Hz$. What is the frequency that the operator hears in the echo reflected from the building (in $\,Hz$)? [Speed of sound is $340 \,m/s$.]

$A$ train moving towards a hill at a speed of $72\ km/hr$ sounds a whistle of frequency $500\ Hz$. $A$ wind is blowing from the hill at a speed of $36\ km/hr$. If the speed of sound in air is $340\ m/s$,the frequency heard by a man on the hill (nearly) is ... $Hz$

$A$ source is stationary and the observer is in motion along a line joining the source and the observer. If the frequency heard by the observer is $1\%$ higher than the true frequency,the ratio of velocity of the observer and that of sound in air is: