Two trains,one coming towards and another going away from an observer,both at $4 \; m/s$,produce a whistle simultaneously of frequency $300 \; Hz$. Find the number of beats produced. (Assume the speed of sound $v = 332 \; m/s$)

$A$ sound wave of frequency $\nu$ travels horizontally to the right. It is reflected from a large vertical plane surface moving to the left with a speed $v$. The speed of sound in the medium is $c$. Then:

When an observer moves towards a stationary source with velocity $V_1$,the apparent frequency of the emitted note is $F_1$. When the observer moves away from the stationary source with velocity $V_1$,the apparent frequency is $F_2$. If $v$ is the velocity of sound in air and $\frac{F_1}{F_2} = 2$,then $\frac{v}{V_1}$ is equal to:

$A$ sound source,emitting sound of constant frequency,moves with a constant speed and crosses a stationary observer. The frequency $(n)$ of sound heard by the observer is plotted against time $(t)$. Which of the following graphs represents the correct variation?

$A$ source of sound whose frequency is $1000 \text{ Hz}$ is moving with a speed of $33 \text{ m/s}$. The waves reflected by a fixed obstacle are registered by a receiver that moves together with the source. If the speed of the sound waves is $330 \text{ m/s}$, then the frequency registered by the receiver is: (in $\text{ kHz}$)

$A$ policeman on duty detects a drop of $10 \%$ in the pitch of the horn of a moving car as it crosses him. If the velocity of sound is $330 \, m/s$,calculate the speed of the car in $m/s$.