$A$ person observes two moving trains,$A$ reaching the station and $B$ leaving the station with equal speed of $30\,m/s$. If both trains emit sounds with frequency $300\,Hz$,(Speed of sound : $330\,m/s$) the approximate difference of frequencies heard by the person will be $..........Hz$.

An engine sounding a whistle of frequency $1152 \ Hz$ is receding from a stationary observer at $72 \ km/h$. If the velocity of sound in air is $340 \ m/s$,then the frequency of the note heard by the observer is: (in $Hz$)

$A$ 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?

$A$ 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 velocity of sound is $340 \,m/s$. $A$ source of sound having a frequency of $90 \,Hz$ is moving towards a stationary observer with a speed of one-tenth that of sound. The apparent frequency of sound as heard by the observer is: (in $\,Hz$)

$A$ submarine $(A)$ travelling at $18\, km/hr$ is being chased along the line of its velocity by another submarine $(B)$ travelling at $27\, km/hr$. $B$ sends a sonar signal of $500\, Hz$ to detect $A$ and receives a reflected sound of frequency $v$. The value of $v$ is close to ... $Hz$ (Speed of sound in water $= 1500\, ms^{-1}$)