Consider two tuning forks with natural frequency $250 \,Hz$. One is moving away and another is moving towards a stationary observer at the same speed. If the observer hears beats of frequency $5 \,Hz$, then the speed of the tuning fork is: (Given, speed of sound wave is $350 \,m/s$.) (in $\,m/s$)

$A$ car travelling at a speed of $54 \ km/h$ towards a wall sounds a horn of frequency $400 \ Hz$. The difference in the frequencies of two sounds, one received directly from the car and the other reflected from the wall, noticed by a person standing between the car and the wall is (speed of sound in air is $335 \ m/s$):

$A$ sound source $S$ is moving along a straight track with speed $v,$ and is emitting sound of frequency $v_{0}.$ An observer is standing at a finite distance,at the point $O,$ from the track. The time variation of frequency heard by the observer is best represented by (where $t_{0}$ represents the instant when the distance between the source and observer is minimum).

$A$ $SONAR$ system fixed in a submarine operates at a frequency of $40.0 \; kHz$. An enemy submarine moves towards the $SONAR$ with a speed of $360 \; km/h$. What is the frequency (in $kHz$) of sound reflected by the submarine (in $; kHz$)? Take the speed of sound in water to be $1450 \; m/s$.

$A$ vehicle with a horn of frequency $n$ is moving with a velocity of $30\, m/s$ in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency $n + n_1$. Then (if the sound velocity in air is $300\, m/s$):

When the 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 source with velocity $V_{1}$,the apparent frequency is $F_{2}$. If $V$ is the velocity of sound in air and $F_{1} / F_{2} = 2$,then $V / V_{1}$ is equal to: