$A$ bat flies at a steady speed of $4 \,ms^{-1}$ emitting a sound of $f = 90 \times 10^{3} \,Hz$. It is flying horizontally towards a vertical wall. The frequency of the reflected sound as detected by the bat will be (take velocity of sound in air is $330 \,ms^{-1}$)

$A$ source at rest emits sound waves of frequency $102 \ Hz$. Two observers are moving away from the source of sound in opposite directions,each with a speed of $10 \%$ of the speed of sound. The ratio of the frequencies of sound heard by the observers is

$A$ train is moving with a constant speed along a large circular track. The engine of the train emits a sound of frequency $f$. What is the frequency heard by the guard at the rear end of the train?

Statement $-1$: Due to the motion of the listener,the frequency of the sound waves (as received by the listener) emitted by a stationary source is affected.
Statement $-2$: Due to the motion of the source,the wavelength of the sound waves (emitted by the source) as received by a stationary listener is affected.
Statement $-3$: If the receiver and the source are both moving,the observed frequency must be different from the original frequency of the source.
Treat the motion of the source or listener as always along the line joining them for all the above cases.

$A$ motorcycle starts from rest and accelerates along a straight path at $2 \; m/s^2$. At the starting point of the motorcycle,there is a stationary electric siren. How far has the motorcycle gone when the driver hears the frequency of the siren at $94 \%$ of its original value (in $; m$)? (Speed of sound $= 330 \; m/s$)

If a source emitting waves of frequency $F$ moves towards an observer with a velocity $V/3$ and the observer moves away from the source with a velocity $V/4$,the apparent frequency as heard by the observer will be ($V=$ velocity of sound).