An engine is moving towards a wall with a velocity $50\, ms^{-1}$ and emits a note of $1.2\, kHz$. The speed of sound in air is $350\, ms^{-1}$. The frequency of the note after reflection from the wall as heard by the driver of the engine is ..... $kHz$.

When the observer moves towards a stationary source with velocity $V_1$, the apparent frequency of the emitted note is $F_1$. When the observer moves away from the source with velocity $V_1$, the apparent frequency is $F_2$. If $V$ is the speed of sound in air and $F_1/F_2 = 2$, then $V/V_1 =$

$A$ person carrying a whistle emitting a note of $272 \text{ Hz}$ is running towards a reflecting surface with a speed of $18 \text{ km/h}$. The speed of sound in air is $345 \text{ m/s}$. 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 $Hz$)

$A$ 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).

$A$ boy standing on a platform observes the frequency of a train horn as it passes by. The change in the frequency noticed as the train approaches and recedes him with a velocity of $108 \text{ km/h}$ is (speed of sound in air $= 330 \text{ m/s}$) (in $\%$)