$A$ source of sound of frequency $500 Hz$ is moving towards an observer with velocity $30 m/s$. The speed of sound is $330 m/s$. The frequency heard by the observer will be .... $Hz$

The wavelength is $120 \, cm$ when the source is stationary. If the source is moving with a relative velocity of $60 \, m/s$ towards the observer,then the wavelength of the sound wave reaching the observer will be ... $cm$ (velocity of sound $= 330 \, m/s$).

Which of the following statements is false?

An observer moves towards a stationary source of sound with a velocity equal to one-fifth of the velocity of sound. The percentage change in the frequency will be $\dots \;$%.

$A$ whistle of frequency $540 Hz$ rotates in a horizontal circle of radius $2 m$ at an angular speed of $15 rad/s$. What is the highest frequency heard by a listener at rest with respect to the center of the circle (in $Hz$)? (Velocity of sound in air $= 330 m/s$)

The frequency changes by $10\%$ as a sound source approaches a stationary observer with constant speed $v_s$. What would be the percentage change in frequency as the source recedes from the observer with the same speed? (Given that $v_s < v$,where $v$ is the speed of sound in air)