A stationary source emits frequency f towards a large reflecting wall moving directly towards the source with speed u. The reflected sound returns to the stationary source. Which expression gives the frequency received back at the source?
Options

Question

A stationary source emits frequency f towards a large reflecting wall moving directly towards the source with speed u. The reflected sound returns to the stationary source. Which expression gives the frequency received back at the source?

Options

G1 Physics · Accepted Answer

The moving wall first acts as an observer approaching the stationary source. Thus the frequency received by the wall is f₁ = f×(v+u)/v. The wall then acts as a moving source of frequency f₁, moving towards the original stationary source. Therefore, fᵣ = f₁×v/(v−u). Hence, fᵣ = [f×(v+u)/v]v/(v−u) = f×(v+u)/(v−u). Correct option: A.