Sound waves of wavelength greater than that of audible sound are called

$A$ stone is dropped into a well that is $19.6\,m$ deep. If the echo is heard after $2.06\,s$ of dropping the stone,calculate the velocity of sound in $m/s$.

$A$ tuning fork makes $256$ vibrations per second in air. When the velocity of sound is $330\, m/s$,the wavelength of the tone emitted is ... $m$.

Which of the following is a longitudinal wave?

The velocity of sound in air at $20^{\circ} C$ and $1 \text{ atm}$ pressure is $344.2 \text{ m/s}$. At $40^{\circ} C$ and $2 \text{ atm}$ pressure, the velocity of sound in air is approximately: (in $\text{ m/s}$)

What is called rarefaction? Which type of changes in density and pressure take place in it?