Question

How far away is the cliff from a child, if the child hears an echo from it $4\text{s}$ after the child blows a powerful horn? The velocity of sound in air at $22{}^{\circ }\text{C}$ is $344\text{m/s}$.

• A. $1000\text{m}$
• B. $1032\text{m}$
• C. $58\text{m}$
• D. $688\text{m}$

Answer 1

The correct option is D $688\text{m}$

Given:
Echo is heard after time, $t=4\text{s}$
Velocity of sound, $v=344\text{m/s}$
When the horn was blown, the sound travels the distance to the cliff i.e., $d$ and then it reflects back to the child.
So the distance traveled by the sound in $4\text{s}$ will be $=2d$
$\because 2d=v\times t$
$⟹2d=344\times 4$
$⟹d=688\text{m}$
So the distance between the child and the cliff is $688\text{m}$.