If y = 0.02 sin (20x - 400t) (SI units), the wave number is

20 (1/m)

Explanation:

Hi there!

The wavenumber k is related to the wavelength λ as:

k = 2π/λ

It appears in wave equations as the argument of the sine or cosine functions and is multiplied by a distance.

In the given equation, if the distance is x, the number 20 must have dimentions of 1/D (D = = distance) which are the dimentions of the wavenumber, if considering SI units, the units of x must be meters, therefore, the units of the wavenumber must be 1/meters

The wavenumber must be: 20 (1/m)