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 ..... $kHz$.

An observer is moving away from a source of sound of frequency $100 \, Hz$. His speed is $33 \, m/s$. If the speed of sound is $330 \, m/s$,then the observed frequency is .... $Hz$.

Two trains move towards each other with the same speed. The speed of sound is $340 \; m/s$. If the pitch of the whistle of one train heard by an observer on the other train changes by a factor of $9/8$,then the speed of each train is ........... $m/s$.

Consider the Doppler effect in two cases. In the first case,an observer moves towards a stationary source of sound with a speed of $50 \,m/s$. In the second case,the observer is at rest and the source moves towards the observer with the same speed of $50 \,m/s$. Then the frequency heard by the observer will be [velocity of sound in air $= 330 \,m/s$.]

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

Consider two sound sources $S_1$ and $S_2$ having the same frequency $100\,Hz$ and the observer $O$ located between them as shown in the figure. All three are moving with the same velocity in the same direction. The beat frequency heard by the observer is .... $Hz$.