An observer starts moving with uniform acceleration $a$ towards a stationary sound source of frequency $f$. As the observer approaches the source,the apparent frequency $f'$ heard by the observer varies with time $t$ as:

$A$ source at rest emits sound waves of frequency $102 \ Hz$. Two observers are moving away from the source of sound in opposite directions, each with a speed of $10 \%$ of the speed of sound. The ratio of the frequencies of sound heard by the observers is

Two cars are approaching each other at an equal speed of $7.2\, km/hr$. When they see each other,both blow horns having a frequency of $676\, Hz$. The beat frequency heard by each driver will be $.....\, Hz$. [Velocity of sound in air is $340\, m/s$.]

$A$ siren emitting a sound of frequency $800 \, Hz$ moves away from an observer towards a cliff at a speed of $15 \, m s^{-1}$. The frequency of sound that the observer hears in the echo reflected from the cliff is .... $Hz$ (Take velocity of sound in air $= 330 \, m s^{-1}$)

$A$ car is moving towards a high cliff. The car driver sounds a horn of frequency $f$. The reflected sound heard by the driver has a frequency $2f$. If $v$ is the velocity of sound,then the velocity of the car,in the same velocity units,will be:

Two sources $A$ and $B$ are sending notes of frequency $680 \ Hz$. $A$ listener moves from $A$ towards $B$ with a constant velocity $u$. If the speed of sound in air is $340 \ ms^{-1}$, what must be the value of $u$ so that he hears $10$ beats per second (in $ms^{-1}$)?