The wavelength of the detected sound when the projectile is at h is:

Explanation:

This is quite a very easy one. Would have been better if it were a question to solve, but then since it isn't.

The wavelength is usually given as the ratio between the speed of the sound, with respect to the frequency of the sound.

Succinctly put, if the speed of the sound is 200 m/s, and it's frequency is 50 Hz, for example. Then the wavelength is

200 / 50 = 4 m.

I hope that's clear?

an ion is a charged atom or molecule. it is charged because the number of electrons do not equal the number of protons in the atom or molecule. an atom can acquire a positive charge or a negative charge depending on whether the number of electrons in an atom is greater or less then the number of protons in the atom.