Does an oscillating source always produce sound waves?

An ultrasonic signal sent from $SONAR$ returns to it after reflection from a rock after a lapse of $1 \, s$. If the velocity of ultrasound in water is $1600 \, m/s$,the depth of the rock in water is ..... $m$.

At what temperature does the velocity of sound in air increase by $10\%$ compared to its velocity at $0^{\circ}C$ (in $^{\circ}C$)?

One Mach number is equal to

$A$ sound is produced by plucking a string in a musical instrument,then

$A$ tuning fork of frequency $220 \,Hz$ produces sound waves of wavelength $1.5 \,m$ in air at $N.T.P$. The increase in wavelength when the temperature of air is $27^{\circ} C$ is nearly $\left(\sqrt{\frac{300}{273}}=1.05\right)$ (in $\,m$)