Which of the following is not a transverse wave?

At what temperature is the velocity of sound double that of its velocity at $0^{\circ}C$?

$A$ person standing on an open ground hears the sound of a jet aeroplane coming from the north at an angle of $60^{\circ}$ with the ground level. However,he finds the aeroplane right vertically above his position. If $\upsilon$ is the speed of sound,what is the speed of the plane?

The wavelength of sound in any gas depends upon

Out of hot moist air and dry cold air,in which does sound travel faster?

$A$ person standing between two parallel cliffs fires a gun and hears two echoes,the first echo after $1 \ s$ and the second echo after $3 \ s$. If the velocity of sound is $340 \ m/s$,the distance between the two cliffs is: (in $m$)