$A$ car sounding a horn of frequency $1200 \text{ Hz}$ passes a stationary observer. The ratio of frequencies of the horn noted by the observer before and after passing the car is $7:5$. If the speed of sound is $V$,the speed of the car is:

The observer is moving with velocity $v_0$ towards the stationary source of sound and then after crossing moves away from the source with velocity $v_0$. Assume that the medium through which the sound waves travel is at rest. If $v$ is the velocity of sound and $n$ is the frequency emitted by the source,then the difference between apparent frequencies heard by the observer is:

$A$ speaker emits a sound wave of frequency $f_0$. When it moves towards a stationary observer with speed $u$,the observer measures a frequency $f_1$. If the speaker is stationary and the observer moves towards it with speed $u$,the measured frequency is $f_2$. Then,

$A$ 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:

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:

Two trucks heading in opposite directions, each with a speed of $0.1 u$, approach each other. The speed of sound is $u$. The driver of the first truck sounds his horn with a frequency of $495 \,Hz$. Let $v_1$ and $v_2$ be the frequencies heard by the driver of the second truck when the trucks are approaching each other and when the trucks have passed each other, respectively. The magnitude of $v_1 - v_2$ is (in $\,Hz$)