$A$ 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 ..... $\text{cycles/sec}$.

$A$ 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 $330 \ m/s$.

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

$A$ car is moving with a speed of $72 \text{ km/h}$ towards a roadside source that emits sound at a frequency of $850 \text{ Hz}$. The car driver listens to the sound while approaching the source and again while moving away from the source after crossing it. If the velocity of sound is $340 \text{ m/s}$, the difference of the two frequencies the driver hears is: (in $\text{ Hz}$)

$A$ train,standing in a station-yard,blows a whistle of frequency $400\; Hz$ in still air. The wind starts blowing in the direction from the yard to the station with a speed of $10\; m s^{-1}$. What are the frequency,wavelength,and speed of sound for an observer standing on the station's platform? Is the situation exactly identical to the case when the air is still and the observer runs towards the yard at a speed of $10\; m s^{-1}$? The speed of sound in still air can be taken as $340\; m s^{-1}$.

$A$ source of sound and a listener are approaching each other with a speed of $40 \, m/s$. The apparent frequency of the note produced by the source is $400 \, cps$. Then,its true frequency (in $cps$) is (velocity of sound in air $= 360 \, m/s$).