$A$ 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 ... $Hz$

Three musicians experiment with the Doppler effect. Musician $A$ rides in a car at a speed $u$ directly away from musician $B$ who is stationary. Musician $C$ rides in a car directly toward $B$ and travels at the same speed as $A$. Musician $A$ plays a note at frequency $f_A$ on his trumpet. $B$ hears the note,adjusts his trumpet,and plays the same note he heard. Choose the incorrect statement.

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 $\,m/s$)

If the source and the observer are both relatively at rest and the speed of sound is increased,then the frequency heard by the observer will:

Two trucks heading in opposite directions, each with a speed of $0.1 u$, approach each other. The speed of sound is $u$. The driver of the first truck sounds his horn with a frequency of $495 \,Hz$. Let $v_1$ and $v_2$ be the frequencies heard by the driver of the second truck when the trucks are approaching each other and when the trucks have passed each other, respectively. The magnitude of $v_1 - v_2$ is (in $\,Hz$)

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 $= 330 \,m/s$):