Single correct option
The persistence of hearing is about 0.1 s. If the speed of sound in air is 344 m/s, the minimum distance of a reflecting surface from the listener for a distinct echo is
- A. 34.4 m
- B. 17.2 m
- C. 8.6 m
- D. 344 m
Show answer and solution
Answer: (B) 17.2 m
The sound must travel to the wall and back within at least 0.1 s, a total of 344 × 0.1 = 34.4 m. The reflector is therefore half of that, 17.2 m, away. The trap is forgetting that the path is a round trip, which leads to 34.4 m.
Saved on this device. Sign in or create a free account to keep it on every device.