$A$ train is approaching a platform with a speed of $10 \,ms^{-1}$ while blowing a whistle of frequency $340 \,Hz$. What is the frequency of the whistle heard by a stationary observer on the platform (in $\,Hz$)? (Given speed of sound $= 340 \,ms^{-1}$)

$A$ vehicle sounding a whistle of frequency $256 \,Hz$ is moving on a straight road towards a hill with a velocity of $10 \,ms^{-1}$. The number of beats per second observed by a person travelling in the vehicle is (velocity of sound $= 330 \,ms^{-1}$).

With what velocity should an observer approach a stationary sound source,so that the apparent frequency of sound appears double the actual frequency? (Let $v$ be the velocity of sound).

$A$ musician on a moving vehicle plays a tone at $880 \ Hz$. When the vehicle is approaching a listener, the listener receives it as an $888 \ Hz$ tone. What is the speed of the vehicle (in $m \ s^{-1}$)? (Assume the velocity of sound is $333 \ m \ s^{-1}$)

$A$ and $B$ are two sources generating sound waves. $A$ listener is situated at $C$. The frequency of the source at $A$ is $500 \, Hz$. $A$ now moves towards $C$ with a speed of $4 \, m/s$. The number of beats heard at $C$ is $6$. When $A$ moves away from $C$ with a speed of $4 \, m/s$,the number of beats heard at $C$ is $18$. The speed of sound is $340 \, m/s$. The frequency of the source at $B$ is ..... $Hz$.

$A$ bus moving with a uniform speed of $72 \,km/h$ towards a building blows a horn of frequency $1.7 \,kHz$. If the speed of sound in air is $340 \,m/s$, what will be the frequency of the echo heard by the bus driver (in $\,kHz$)?