Question

1. A boy stands at a distance of 170 m from a cliff. He claps his hand and hears an echo If the
speed of sound in air is 340 m/s, after how long does he hear his echo?​

Answer 1

Answer:

Distance of the boy from the cliff = 170m

speed of sound = 340m/s=v

The time taken by the sound to travel the distance till the cliff and back again = t

2d=v×t

$2 \times 170 = 340 \times t$

$340 = 340 \times t$

$therefore \: \: \\ t = 340 \div 340 = 1second$

Answer 2

Answer:

An echo is heard after  $1$ $sec$  by the boy.

Explanation:

• When a person produces a sound and then hears a sound that is reflected by some hard obstruction material, the phenomenon is called an echo.
• The received sound depends on the speed of sound in the air and the distance of the obstruction from the person.

The formula used to calculate the time to hear an echo:

$T=\frac{2D}{s}$

where, $D$ is the obstruction's distance from the person.

            $s$  is the sound's speed in air.

The distance traveled by the sound, $2D=2$ × $170$ $m$

                                                                   $=340$ $m$

The sound's speed, $s=340$ $m/s$

So, echo is heard after time  $=\frac{340m}{340m/s}$

                                                $= 1$ $sec$

Hence, an echo is heard after $1$ $sec$.