$A$ bat is flitting about in a cave,navigating via ultrasonic beeps. Assume that the sound emission frequency of the bat is $40\; kHz$. During one fast swoop directly toward a flat wall surface,the bat is moving at $0.03$ times the speed of sound in air. What frequency (in $kHz$) does the bat hear reflected off the wall?

$A$ car blowing a horn of frequency $350\, Hz$ is moving towards a wall with a speed of $5\, m/s$. The beat frequency heard by a person standing between the car and the wall is ..... $Hz$ (speed of sound in air $= 350\, m/s$).

$A$ 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 ... $\text{ Hz}$.

$A$ stationary source of sound $A$ is producing sound of frequency $170 \, Hz$. Another source of sound $B$ producing sound of frequency $240 \, Hz$ is moving towards the source $A$ on a straight path with a uniform speed of $20 \, ms^{-1}$. An observer between $A$ and $B$ is moving towards the source $A$ along the straight path $BA$. If the number of beats heard by the observer is zero, the speed of the observer is . . . . . . $ms^{-1}$. (Speed of sound in air $= 340 \, ms^{-1}$).

$A$ motorcyclist is moving around a circular track of radius $50 \ m$ with a constant speed of $25 \ m/s$. $A$ static siren at point $Y$ emits sound of frequency $n$. How many times (approximately) in an hour will the motorcyclist hear the sound of the actual frequency $n$?

$A$ siren emitting sound of frequency $500 \; Hz$ is going away from a static listener with a speed of $50 \; m/s$. The frequency of sound heard by the listener is .... $Hz$. (Take speed of sound $v = 330 \; m/s$)