Question

Calculate the minimum distance at which a person should stand in front of a reflecting surface so that he can hear a distinct echo.

(Take speed of sound in air = 350⁢ ms⁻¹.)

Answer 1

For a distinct echo, the reflected sound must reach the ear at least 0.1 s after the original sound.

Given: \[ v=350\ \text{m s}^{-1}\]

\[t=0.1\ \text{s} \]

\[d=\frac{vt}{2}\]

\[=\frac{350\times0.1}{2}\]

\[=\frac{35}{2}\]

= 17.5 m