A girl claps her hands in front of a tall wall and hears the echo 0.8 s later. If the speed of sound in air is 340 m/s, how far is the wall from her?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 136 m
In an echo, the sound goes to the wall and comes back, so it travels twice the distance to the wall.
Speed of sound: \(v = 340\,\mathrm{m/s}\); time for the echo: \(t = 0.8\,\mathrm{s}\)
Total distance travelled by the sound \(= v \times t = 340 \times 0.8 = 272\,\mathrm{m}\)
Distance of the wall \(d = \frac{272}{2}\)
\(d = 136\,\mathrm{m}\)