$SONAR$ emits which of the following waves?

The wavelength of ultrasonic waves in air is of the order of

The ratio of densities of nitrogen and oxygen is $14:16$. The temperature at which the speed of sound in nitrogen will be the same as that in oxygen at $55^oC$ is ..... $^oC$.

$A$ source of sound of frequency $600 Hz$ is placed inside water. The speed of sound in water is $1500 m/s$ and in air is $300 m/s.$ The frequency of sound recorded by an observer who is standing in air is .... $Hz$

The speed of a longitudinal wave in a metallic bar is $400 \ m/s$. If the density and Young's modulus of the bar material are increased by $0.5\%$ and $1\%$ respectively, then the speed of the wave is changed approximately to . . . . . . $m/s$.

$A$ 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 $m$)