UPSC 2016 CDS I GK Paper

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, the wall from him is 51 m. An echo is the sound we hear when we 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 = the distance the sound wave travelled back and forth. The distance of the wall from the person will be half of this.
Required distance =d/=

102.

2

=51m