What is the distance between consecutive condensation and rarefaction in longitudinal waves?

When a steel pipe is hammered at one end,we hear two sounds at another end. Why?

$A$ source of sound $S$ having frequency $f$. Wind is blowing from source to observer $O$ with velocity $u$. If the speed of sound with respect to air is $C$,the wavelength of sound detected by $O$ is:

What is the effect of humidity on sound waves when humidity increases?

Two monoatomic ideal gases $1$ and $2$ of molecular masses $m_1$ and $m_2$ respectively are enclosed in separate containers kept at the same temperature. The ratio of the speed of sound in gas $1$ to that in gas $2$ is given by

At what temperature (in $^\circ C$) will the speed of sound in air be $3$ times its value at $0^\circ C$ (in $^\circ C$)?