$A$ train blowing its whistle moves with constant speed on a straight track towards an observer and then crosses him. If the ratio of the difference between the actual and apparent frequencies is $3:2$ in the two cases (approaching and receding),then the speed of the train is (where $v$ is the speed of sound).

$A$ train is moving towards a stationary observer with speed $34 \text{ m/s}$. $A$ train sounds a whistle of frequency $450 \text{ Hz}$. If the speed of sound is $340 \text{ m/s}$, the frequency heard by the observer in Hz is

$A$ bat moving at $10\,ms^{-1}$ towards a wall sends a sound signal of $8000\,Hz$ towards it. On reflection it hears a sound of frequency $f$. The value of $f$ in $Hz$ is close to (speed of sound $= 320\,ms^{-1}$)

An observer is standing $500 \,m$ away from a vertical hill. Starting between the observer and the hill, a police van sounding a siren of frequency $1000 \,Hz$ moves towards the hill with a uniform speed. If the frequency of the sound heard directly from the siren is $970 \,Hz$, the frequency of the sound heard after reflection from the hill (in $Hz$) is about, (velocity of sound $= 330 \,m/s$):

$A$ person observes two moving trains. Train $A$ is reaching the station and train $B$ is leaving the station, both with an equal speed of $30 \text{ m/s}$. If both trains emit sounds with a frequency of $300 \text{ Hz}$, and the speed of sound is $330 \text{ m/s}$, what is the difference in the frequencies heard by the person (in $\text{ Hz}$)?

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