$A$ source emits a sound of frequency $400 \ Hz$,but the listener hears it to be $390 \ Hz$. Then:

$A$ 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 $= 343\,m/s$)

An engine is moving on a circular path of radius $200 \,m$ with a speed of $15 \,m/s$. What will be the frequency heard by an observer who is at rest at the centre of the circular path,when the engine blows the whistle with a frequency of $250 \,Hz$?

An engine giving a whistle is moving towards a stationary observer with a speed of $110\, m/s$. What will be the ratio of the frequency of the whistle heard when the engine is approaching and receding from the observer? (Speed of sound $= 330\, m/s$)

$A$ locomotive approaching a crossing at a speed of $20 \, m/s$ sounds a whistle of frequency $640 \, Hz$ when it is $1 \, km$ from the crossing. There is no wind and the speed of sound in air is $330 \, m/s$. What frequency is heard by an observer located $\sqrt{3} \, km$ away from the crossing on a straight road at a right angle to the locomotive's path (in $, Hz$)?

An observer starts moving with uniform acceleration $a$ toward a stationary sound source emitting a whistle of frequency $n$. As the observer approaches the source,the apparent frequency $n'$ heard by the observer varies with time $t$ as: