Two trains are moving towards each other at speeds of $20 \, m/s$ and $15 \, m/s$ relative to the ground. The first train sounds a whistle of frequency $600 \, Hz$. The frequency of the whistle heard by a passenger in the second train before the trains meet is ...... $Hz$ (the speed of sound in air is $340 \, m/s$).

$A$ sound source is moving on a circular path of radius $R$ with constant angular speed $\omega$ in an anticlockwise direction and emits a frequency $n$. An observer performs simple harmonic motion along the path $QPR$ with time period $T = \frac{2\pi}{\omega}$ as shown in the figure. If at $t = 0$ the source is at $A$ and the observer is at $Q$,and assuming $OP$ is very large compared to the radius $R$ and $QP$,then:

$A$ train is moving with a uniform speed $33 \ m/s$ and an observer is approaching the train with the same speed. If the train blows a whistle of frequency $1000 \ Hz$ and the velocity of sound is $333 \ m/s$, then the apparent frequency of the sound that the observer hears is: (in $Hz$)

The driver of a car travelling with a speed $V_1 \ m/s$ towards a wall sounds a siren of frequency $n \ Hz$. If the velocity of sound in air is $V \ m/s$,then the frequency of the sound reflected from the wall and as heard by the driver in $Hz$ is

$A$ policeman on duty detects a drop of $10 \%$ in the pitch of the horn of a moving car as it crosses him. If the velocity of sound is $330 \, m/s$,calculate the speed of the car in $m/s$.

$A$ 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 .... $\%$