A child hears an echo from a cliff 4 seconds after the sound from a powerful cracker is produced. How far away is the cliff from the child? Velocity of sound in air at $20^{\circ} C$ is 344 m/s :

688 m

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1376 m

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344 m

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244 m

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Solution

The correct option is D $688 m$
Velocity of sound in air $v = 344 m / s$
Let the distance between the cliff and the child be $x$ .
The sound has to travel to the cliff and get reflected back to the child itself, thus total distance travelled by the sound is $2 x$ .
Time taken to hear an echo $t = 4$ s
So, $2 x = v t$
Or $2 x = 344 \times 4$
$⟹ x = 688 m$

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Similar questions

(a) What is an echo? How is echo formed?

(b) What is the minimum distance in air required from a sound reflecting surface to hear an echo (at $20^{o}$ C)?

(c) A man standing 825 metres away from a cliff (steep rock) fires a gun. After how long will he hear its echo? The speed of sound in air is $330 m / s$ .

Q. (i) What is the principle on which SONAR is based?
(ii) An observer stands at a certain distance away from a cliff and produces a loud sound. He hears the echo of the sound after

1.8 s

. Calculate the distance between the cliff and the observer if the velocity of sound in air is

340 m s^{- 1}

Q. A siren emitting a sound of frequency

800 H z

moves away from an observer towards a cliff at a speed of

15 {m s}^{- 1}

. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is
(Take velocity of sound in air

= 330 {m s}^{- 1}

)

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A child hears an echo from a cliff 4 seconds after the sound from a powerful cracker is produced. How far away is the cliff from the child? Velocity of sound in air at 20∘C is 344 m/s :

A child hears an echo from a cliff 4 seconds after the sound from a powerful cracker is produced. How far away is the cliff from the child? Velocity of sound in air at $20^{\circ} C$ is 344 m/s :