A person rings a metallic bell near a strong concrete wall. He hears the echo after 0.3 s. If the sound moves with a speed of 340 m/s, how far is the wall from him?
- 102 m
- 11 m
- 51 m
- 30 m
An echo is the sound you hear when you make a noise and the sound wave reflects off a distant object. The sound wave travels in a straight line. When the wave hits a solid wall, it is reflected.
d = v × t = 340 m/s × 0.3 s
d = 102 m
d is the distance the sound wave traveled back and forth. The distance of the wall from the person will be half of this.
Required distance = d/2 = 102/2 = 51 m
The correct option is C.