A sound is produced between two vertical parallel walls. The echo from one wall is heard after 2 s while…
A sound is produced between two vertical parallel walls. The echo from one wall is heard after 2 s while from the other 2 s after the first echo. The speed of sound in air is $340\text{ ms}^{-1}$. Then,
the distance between two walls is 680 m
the distance between two walls is 1020 m
the next echo will be heard after 8 s from the instant original sound was produced
None of the above
Solution
According to question, $2d_1 = 340 \times t_1$
[Diagram shows a sound source $S$ located between two parallel walls $W_1$ and $W_2$ at distances $d_1$ and $d_2$.]
$\therefore d_1 = 340\text{ m}$ ($t_1 = 2\text{ s}$)
$2d_2 = 340 \times t_2$
$\therefore d_2 = 680\text{ m}$ ($t_2 = t_1 + 2 = 4\text{ s}$)
$\therefore$ Distance between walls $= d_1 + d_2 = 1020\text{ m}$
Next echo will be heard at $6\text{ s}$ not at $8\text{ s}$. Because sound wave reflected from wall $W_2$ will be reflected again by wall $W_1$ in next $2\text{ s}$.