Question

If a child hears an echo from a cliff 6 seconds after the sound produced by shouting, how far is the cliff?
Assume speed of sound in air to be 343 m/s.

• A. 58 m
• B. 1029 m
• C. 68 m
• D. 990 m

Answer 1

The correct option is B 1029 m

Let the distance between the child and the cliff be $d$
Then, the distance traveled by the echo is: $s=2d$

Speed of sound in air, $v=343m{s}^{-1}$
Time to hear echo, $t=6s$

Using the formula for speed,
$v=\frac{s}{t}$
$v=\frac{2d}{t}$
$d=\frac{vt}{2}$
$d=\frac{343\times 6}{2}m$
$d=1029m$