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 ........... $m/s$.

$A$ police car moving at $22 \ m/s$ chases a motorcyclist. The policeman sounds his horn at $176 \ Hz$,while both of them move towards a stationary siren of frequency $165 \ Hz$. Calculate the speed of the motorcycle,if it is given that he does not observe any beats. (in $m/s$)

$A$ whistle emitting a loud sound of frequency $540 \,Hz$ is whirled in a horizontal circle of radius $2 \,m$ at a constant angular speed of $15 \,rad/s$. The speed of sound is $330 \,m/s$. The ratio of the highest to the lowest frequency heard by a listener standing at rest at a large distance from the centre of the circle is

Two cars $X$ and $Y$ are approaching each other with velocities $36 \; km/h$ and $72 \; km/h$ respectively. The frequency of a whistle sound emitted by a passenger in car $X$,heard by the passenger in car $Y$,is $1320 \; Hz$. If the velocity of sound in air is $340 \; m/s$,the actual frequency of the whistle sound produced 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?

$A$ sound source $S$ is moving along a straight track with speed $v,$ and is emitting sound of frequency $v_{0}.$ An observer is standing at a finite distance,at the point $O,$ from the track. The time variation of frequency heard by the observer is best represented by (where $t_{0}$ represents the instant when the distance between the source and observer is minimum).