$A$ train standing at the outer signal of a railway station blows a whistle of frequency $400\, Hz$ in still air. What is the frequency of the whistle for a platform observer when the train recedes from the platform with a speed of $10\, m/s$? (Speed of sound $= 340\, m/s$)

$A$ train approaching a railway crossing at a speed of $120 \ km/h$ sounds a whistle of frequency $576 \ Hz$,when it is $288 \ m$ away from the crossing. The frequency heard by an observer standing on the road perpendicular to the track at a distance of $384 \ m$ from the crossing is (Speed of sound in air $= 340 \ m/s$): (in $Hz$)

An obstacle is moving towards the source with velocity $v$. The sound is reflected from the obstacle. If $c$ is the speed of sound and $\lambda$ is the wavelength,then the wavelength of the reflected wave $(\lambda_{r})$ is

$A$ car is moving at a velocity of $17 \ m/s$ towards an approaching bus that blows a horn at a frequency of $640 \ Hz$ on a straight track. The frequency of this horn appears to be $680 \ Hz$ to the car driver. If the velocity of sound in air is $340 \ m/s$, then the velocity of the approaching bus is: (in $m/s$)

$A$ car sounding a horn of frequency $1000 \,Hz$ passes a stationary observer. The ratio of frequencies of the horn noted by the observer before and after passing of the car is $11:9$. The speed of the car is (Speed of sound $v = 340 \,ms^{-1}$) (in $\,ms^{-1}$)

$A$ source and a detector move away from each other in the absence of wind with a speed of $20 \, m/s$ with respect to the ground. If the detector detects a frequency of $1800 \, Hz$ of the sound coming from the source,then the original frequency of the source,considering the speed of sound in air to be $340 \, m/s$,will be (in $Hz$):