A stone is dropped in a well of depth $500$ m and a sound is heard after $80 / 7$ seconds. Then speed of sound is: $[g = 10 m / s^{2}]$

300

m/s

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350

m/s

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400

m/s

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330

m/s

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Solution

The correct option is B $400$ m/s
here, $S = - 500 m$ [ we take reference level is in initial position of stone]

$u = 0, a = - g = - 10$

use formula , $S = u t + \frac{1}{2} a t^{2}$

$- 500 = 0 - \frac{1}{2} \times 10 \times t^{2}$

$t^{2} = 100 => t = 10 s e c$

but sound is heard after $45 / 4 = 11.25 s e c$

hence, time taken to reach $500 m$ depth = $11.25 - 10 = 1.25 s e c$ .

now speed of sound = distance/time

= $500 / 1.25 = 400 m / s$

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A stone is dropped in a well of depth 500m and a sound is heard after 80/7 seconds. Then speed of sound is: [g=10m/s2]

A stone is dropped in a well of depth $500$ m and a sound is heard after $80 / 7$ seconds. Then speed of sound is: $[g = 10 m / s^{2}]$