$A$ source and an observer move away from each other with the same velocity of $10 \,ms^{-1}$ with respect to the ground. If the observer finds the frequency of sound coming from the source as $1980 \,Hz$, then the actual frequency of the source is (speed of sound in air $= 340 \,ms^{-1}$). (in $\,Hz$)

Doppler's effect will not be applicable when the velocity of sound source is

$A$ car moving towards a cliff emits sound of frequency '$n$'. If the difference in frequencies of the horn and its echo heard by the driver of the car is $10 \%$ of '$n$',then the speed of the car is nearly (Speed of sound in air is $336 \ m/s$) (in $m/s$)

$A$ police van,moving at $22 \, m/s$,chases a motorcyclist. The policeman sounds a horn at $176 \, Hz$,while both of them move towards a stationary siren of frequency $165 \, Hz$ as shown in the figure. If the motorcyclist does not observe any beats,his speed must be .... $m/s$ (take the speed of sound $= 330 \, m/s$).

$A$ 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 $Hz$)

The speed of sound in air at a given temperature is $350 \, m/s$. An engine blows a whistle at a frequency of $1200 \, cps$. It is approaching the observer with a velocity of $50 \, m/s$. The apparent frequency in $cps$ heard by the observer will be: