The driver of a bus approaching a big wall notices that the frequency of his bus's horn changes from $420\, Hz$ to $490\, Hz$,when he hears it after it gets reflected from the wall. Find the speed of the bus (in $kmh^{-1}$) if the speed of sound is $330\, ms^{-1}$.

$A$ source emitting sound of frequency $288 \,Hz$ is tied to a string of $100 \,cm$ length and rotated with an angular velocity of $20 \,rad/s$ in the horizontal plane. The range of frequencies heard by an observer standing at a distance of $5 \,m$ from the source is (in $Hz$) (Speed of sound in air $= 340 \,m/s$)

$A$ source with a frequency of $500 \,Hz$ moves towards a stationary observer with a velocity of $30 \,m/s$. What frequency (in $Hz$) will the observer hear? (The speed of sound in air is $330 \,m/s$.)

The difference between the apparent frequency of a source of sound as perceived by an observer during its approach and recession is $2\%$ of the natural frequency of the source. If the velocity of sound in air is $300 \, m/s$,the velocity of the source is ... $m/s$ (Given that velocity of source < velocity of sound).

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

An Indian submarine $(I)$ and an enemy submarine $(E)$ move towards each other in motionless water. The Indian submarine moves at $50 \ km/h$,and the enemy submarine at $70 \ km/h$. The Indian submarine sends out a sonar signal (sound wave in water) at $1000 \ Hz$. The sonar wave reflects off the enemy submarine and returns to the Indian submarine. If the speed of sound in water is $5500 \ km/h$,what is the frequency of the reflected signal detected by the Indian submarine in $kHz$ (in $kHz$)?