$A$ source with a frequency of $500 \,Hz$ moves towards a stationary observer with a velocity of $30 \,m/s$. What frequency (in $Hz$) will the observer hear? (The speed of sound in air is $330 \,m/s$.)

$A$ police car horn emits a sound at a frequency $240 \text{ Hz}$ when the car is at rest. If the speed of sound is $330 \text{ m/s}$,the frequency heard by an observer who is approaching the car at a speed of $11 \text{ m/s}$ is ... $\text{ Hz}$.

When an observer moves towards a stationary source with velocity $V_1$,the apparent frequency of the emitted note is $F_1$. When the observer moves away from the stationary source with velocity $V_1$,the apparent frequency is $F_2$. If $v$ is the velocity of sound in air and $\frac{F_1}{F_2} = 2$,then $\frac{v}{V_1}$ is equal to:

$A$ source with a frequency of $90 \, \text{vibrations/sec}$ moves towards a stationary observer with a velocity of $1/10 \, V$, where $V$ is the speed of sound. What frequency will the observer hear in $\text{vibrations/sec}$?

Doppler's effect will not be applicable when the velocity of sound source is

What is the Doppler effect? Write its example and explain how its analysis can be performed.