Answer: f(v+vs)/(v-vs).
- A f(v+vs)/(v-vs)
- B f(v-vs)/(v+vs)
- C f x v/(v-vs)
- D f(v+vs)/v
Correct answer: A. f(v+vs)/(v-vs)
Explanation: Wall receives: f' = f x v/(v-vs). Wall reflects back, source now moves toward its own reflected sound: f<sub>heard</sub> = f' x (v+vs)/v = f(v+vs)/(v-vs).
A standing wave forms from two identical waves travelling in opposite directions and interfering; nodes (always zero displacement) and antinodes (maximum displacement) stay fixed in place, unlike a travelling wave where the whole pattern moves.
Concept context
Wave types, superposition, standing waves, Doppler effect, and sound intensity.