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

$A$ train approaching a railway platform with a speed of $20 \ ms^{-1}$ starts blowing the whistle. The speed of sound in air is $340 \ ms^{-1}$. If the frequency of the emitted sound from the whistle is $640 \ Hz$,the frequency of sound to a person standing on the platform will appear to be: (in $Hz$)

$A$ source of sound is moving with a velocity of $50 \ m/s$ towards a stationary observer. The observer measures the frequency of sound as $500 \ Hz$. The apparent frequency of sound as heard by the observer when the source is moving away from him with the same speed is (Speed of sound at room temperature $350 \ m/s$). (in $Hz$)

$A$ source of sound is moving towards a stationary observer with $\frac{1}{10}$ of the speed of sound. The ratio of apparent to real frequency is

$A$ siren placed at a railway platform is emitting sound of frequency $5 \text{ kHz}$. $A$ passenger sitting in a moving train $A$ records a frequency of $5.5 \text{ kHz}$ while the train approaches the siren. During his return journey in a different train $B$,he records a frequency of $6.0 \text{ kHz}$ while approaching the same siren. The ratio of the velocity of train $B$ to that of train $A$ is

$A$ locomotive approaching a crossing at a speed of $20 \, m/s$ sounds a whistle of frequency $640 \, Hz$ when it is $1 \, km$ from the crossing. There is no wind and the speed of sound in air is $330 \, m/s$. What frequency is heard by an observer located $\sqrt{3} \, km$ away from the crossing on a straight road at a right angle to the locomotive's path (in $, Hz$)?