$A$ motor-cyclist moving towards a huge cliff with a speed of $18 \ kmh^{-1}$,blows a horn of source frequency $325 \ Hz$. If the speed of the sound in air is $330 \ ms^{-1}$,the number of beats heard by him is

$A$ train approaching a railway crossing at a speed of $120 \ km/h$ sounds a whistle of frequency $576 \ Hz$,when it is $288 \ m$ away from the crossing. The frequency heard by an observer standing on the road perpendicular to the track at a distance of $384 \ m$ from the crossing is (Speed of sound in air $= 340 \ m/s$): (in $Hz$)

$A$ person with a vibrating tuning fork of frequency $338 \,Hz$ is moving towards a vertical wall with a speed of $2 \,ms^{-1}$. The velocity of sound in air is $340 \,ms^{-1}$. The number of beats heard by that person per second is

$A$ source of sound emits waves with frequency $f \, Hz$ and speed $V \, m/s$. Two observers move away from this source in opposite directions,each with a speed $0.2V$ relative to the source. The ratio of frequencies heard by the two observers will be

$A$ whistle of frequency $500 \, Hz$ tied to the end of a string of length $1.2 \, m$ revolves at $400 \, rev/min$. $A$ listener standing some distance away in the plane of rotation of the whistle hears frequencies in the range (speed of sound $= 340 \, m/s$):

$A$ source of sound emitting a note of frequency $200 Hz$ moves towards an observer with a velocity $v$ equal to the velocity of sound. If the observer also moves away from the source with the same velocity $v$,the apparent frequency heard by the observer is .... $Hz$