You have a 40-Hz sound wave and a 5,000-Hz sound wave. Both are traveling
through steel. Which sound wave will travel faster?

Both sound waves will travel at the same speed.

Explanation:

The speed of sound depends only on the density and the elastic properties of the medium it is travelling through, the mathematical relation is

,

where is the bulk modulus (a measure of how much a material will compress under a certain pressure), and is the density of the medium.

Since the frequency of a sound wave does not change the properties of the medium it is travelling through, every frequency will have the same speed through a certain medium.

Hence, a 5,000 Hz and a 40-Hz sound wave will have the same speed through steel.

snell's law

refractve index = sin incidence / sin refraction