The Poynting vector S⃗ S→S_vec gives the energy flux per unit area of electromagnetic waves. It is defined by the relation S⃗ =E⃗ ×B⃗ μ0S→=E→×B→μ0. Calculate the time-averaged Poynting vector ⟨S⃗ ⟩⟨S→⟩ of the wave considered in this problem.

The fundamental frequency of the slinky = 8Hz

An input frequency of 28 Hz will not create a standing wave

Explanation:

Let Fo = fundamental frequency

At third harmonic,

F = 3Fo

If F = 24Hz

24 = 3Fo

Fo = 24/3 = 8Hz

If an input frequency = 28 Hz at 3rd harmonic

Let find the fundamental frequency

28 = 3Fo

Fo = 28/3

Fo = 9.33333Hz

Since Fo isn't a whole number, it can't create a standing wave