$A$ train is moving on a straight track with speed $20 \ ms^{-1}$. It is blowing its whistle at a frequency of $1000 \ Hz$. The percentage change in the frequency heard by a person standing near the track as the train passes him is (speed of sound $= 320 \ ms^{-1}$) close to .... $\%$

Consider two tuning forks with natural frequency $250 \,Hz$. One is moving away and another is moving towards a stationary observer at the same speed. If the observer hears beats of frequency $5 \,Hz$, then the speed of the tuning fork is: (Given, speed of sound wave is $350 \,m/s$.) (in $\,m/s$)

$A$ train moving towards a hill at a speed of $72\ km/hr$ sounds a whistle of frequency $500\ Hz$. $A$ wind is blowing from the hill at a speed of $36\ km/hr$. If the speed of sound in air is $340\ m/s$,the frequency heard by a man on the hill (nearly) is ... $Hz$

$A$ train is moving towards a stationary observer (at $t = 0$) with a constant velocity of $20 \ m/s$ and after some time it crosses the observer. Which of the following curves best represents the frequency $f$ received by the observer as a function of time?

If a source emitting waves of frequency $F$ moves towards an observer with a velocity $V/3$ and the observer moves away from the source with a velocity $V/4$,the apparent frequency as heard by the observer will be ($V=$ velocity of sound).

$A$ train sounding a whistle of frequency $510 \,Hz$ approaches a station at $72 \,km/hr$. The frequency of the note heard by an observer on the platform as the train $(1)$ approaches the station and then $(2)$ recedes from the station are respectively (in hertz) (velocity of sound in air $= 320 \,m/s$).