In $SONAR$, we use

How does a stretched string,on being set into vibration,produce an audible sound?

Given that sound travels in air at $340 \, m s^{-1}$,find the wavelength of the waves in air produced by a $20 \, Hz$ sound source. If the same source is put in a water tank,what would be the wavelength of the sound waves in water? (Given,speed of the sound in water $= 1480 \, m s^{-1}$)

What is Galton's whistle? To what use can it be put?

State whether the following statement is true or false: The velocity of sound in air is higher for higher frequencies than for lower frequencies.

$A$ person fires a gun standing at a distance of $55 \, m$ from a wall. If the speed of sound is $330 \, m s^{-1}$,find the time taken for an echo to be heard. (in $s$)