Answer: 17 m.
- A 17 m
- B 34 m
- C 51 m
- D 68 m
Correct answer: A. 17 m
Explanation: Echo time = 2d/v >= 0.1 s. d >= 0.1 x 340/2 = 17 m.
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.