Question

The sound emitted by a source returns back, after reflection, from a surface after a time interval of $0.5$ seconds. What is the distance between the source and the reflecting surface? (Speed of sound in air is $340\text{m/s}$)

• A. $85\text{m}$
• B. $170\text{m}$
• C. $255\text{m}$
• D. $340\text{m}$

Answer 1

The correct option is A $85\text{m}$

Given,
Time taken for the sound to return back to the source, $\text{t}=0.5\text{s}$
Speed of sound, $\text{v}=340\text{m/s}$
Let $d$ be the distance between the source of sound and the reflecting surface.
The sound emitted by the source travels from the source to the reflecting surface and is reflected back by the surface to the source.
Hence, the total distance travelled by the sound will be $2d$.
Speed of sound $=\frac{\text{Distance travelled}}{\text{Time taken}}$
$340=\frac{2d}{0.5}$
$2d=340\times 0.5=170$
$d=85\text{m}$
Therefore, the distance between the source and the reflecting surface is $85\text{m}$.