$A$ person observes two moving trains. The first reaches the station and the second leaves the station,both with an equal speed of $30 \ m/s$. If both trains emit sounds of frequency $300 \ Hz$,what is the difference in frequencies heard by the person (in $Hz$)? (Speed of sound in air $= 330 \ m/s$)

$A$ person is observing two trains,one coming towards him and the other leaving with the same speed $4\, m/s$. If their whistling frequencies are $240\, Hz$ each,then the number of beats per second heard by the person will be: (if the velocity of sound is $320\, m/s$)

$A$ train moving at a speed of $220\, m s^{-1}$ towards a stationary object,emits a sound of frequency $1000\, Hz$. Some of the sound reaching the object gets reflected back to the train as an echo. The frequency of the echo as detected by the driver of the train is ...... $Hz$. (Speed of sound in air is $330\, m s^{-1}$)

$A$ source and a listener are both moving towards each other with a speed of $v/10$,where $v$ is the speed of sound. If the frequency of the note emitted by the source is $f$,the frequency heard by the listener would be nearly:

$A$ 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:

$A$ train is moving towards a stationary observer. Which of the following curves best represents the frequency $f$ received by the observer as a function of time $t$?