Single correct option
The minimum distance of a reflecting wall from a person, so that the person can hear a distinct echo, is nearly (speed of sound in air = 340 m/s, persistence of hearing = 0.1 s)
- A. 34 m
- B. 17 m
- C. 170 m
- D. 3.4 m
Show answer and solution
Answer: (B) 17 m
The sound must travel to the wall and back in at least 0.1 s. Total path = 340 × 0.1 = 34 m, so the wall must be at least half of it, 17 m, away. The trap is 34 m, which forgets that the sound covers the distance twice.
Saved on this device. Sign in or create a free account to keep it on every device.