One Mach number is equal to

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

The particle displacement of a travelling longitudinal wave is represented by $\xi = \xi(x, t)$. The midpoints of a compression zone and an adjacent rarefaction zone are represented by the letters $C$ and $R$. Which of the following is true?

Which of the following waves cannot be polarized?

$A$ bat emits ultrasonic sound of frequency $1000 \; kHz$ in air. If the sound meets a water surface,what is the wavelength of
$(a)$ the reflected sound,
$(b)$ the transmitted sound?
Speed of sound in air is $340 \; m/s$ and in water is $1486 \; m/s$.

Which of the following is not a transverse wave?