$A$ 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 $= 330 \, m/s$).

An observer moves towards a stationary source of sound with a velocity one-fifth of the velocity of sound. The percentage change in the apparent frequency is ..... $\%$

$A$ whistle sends out $256$ waves in a second. If the whistle approaches the observer with a velocity equal to $\frac{1}{3}$ of the velocity of sound in air,calculate the number of waves per second the observer will receive.

$A$ source of sound $A$ emitting waves of frequency $1800\,Hz$ is falling towards the ground with a terminal speed $v.$ The observer $B$ on the ground directly beneath the source receives waves of frequency $2150\,Hz.$ The source $A$ receives waves,reflected from the ground,of frequency nearly ..... $Hz$ (Speed of sound $= 343\,m/s$)

Doppler shift in frequency does not depend upon:

$A$ car $P$ approaching a crossing at a speed of $10 \, m/s$ sounds a horn of frequency $700 \, Hz$ when $40 \, m$ in front of the crossing. The speed of sound in air is $340 \, m/s$. Another car $Q$ is at rest on a road which is perpendicular to the road on which car $P$ is reaching the crossing. The driver of car $Q$ hears the sound of the horn of car $P$ when he is $30 \, m$ in front of the crossing. The apparent frequency heard by the driver of car $Q$ is ..... $Hz$.