An engine giving a whistle is moving towards a stationary observer with a speed of $110\, m/s$. What will be the ratio of the frequency of the whistle heard when the engine is approaching and receding from the observer? (Speed of sound $= 330\, m/s$)

$A$ source of sound of frequency $90 \text{ vibrations/sec}$ is approaching a stationary observer with a speed equal to $1/10$ the speed of sound. What will be the frequency heard by the observer in $\text{vibrations/sec}$?

$A$ source is stationary and the observer is in motion along a line joining the source and the observer. If the frequency heard by the observer is $1\%$ higher than the true frequency,the ratio of velocity of the observer and that of sound in air is:

$A$ 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 travelling towards a stationary observer. The frequency of sound heard by the observer is three times the original frequency. If the velocity of sound is $v \ m/s$,the speed of the source will be:

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).