Sam was pulling water from a well of depth 80 m, when the key from his pocket fell into it. After how much time he would hear the sound of the metal key falling.
Take speed of sound is 320 ms $^{- 1}$ and g =10 ms $^{- 2}$ .

4 seconds

No worries! We‘ve got your back. Try BYJU‘S free classes today!

4.25 seconds

Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses

4.5 seconds

No worries! We‘ve got your back. Try BYJU‘S free classes today!

4.75 seconds

No worries! We‘ve got your back. Try BYJU‘S free classes today!

Open in App

Solution

The correct option is B 4.25 seconds
Given,
Initial velocity, $u = 0$
Acceleration due to gravity, $g = 10 m s^{- 2}$
Speed of sound, $v_{s o u n d} = 320 m s^{- 1}$
Depth of well, $D = 80 m$
Let,
$T_{1}$ = Time taken by the stone to reach the bottom
$T_{2}$ = Time taken by sound to reach the top of the well

From second equation of motion, we have,
$s = u t + \frac{1}{2} a t^{2}$
$80 = \frac{1}{2} \times 10 \times T_{1}^{2}$

$T_{1}$ = $\sqrt{2 \times \frac{80}{10}}$ = $\sqrt{16} = 4 s e c o n d s$

We know, $T i m e = \frac{D i s t a n c e}{S p e e d}$
$\Rightarrow$ $T_{2}$ = $\frac{80}{320} = 0.25 s e c o n d s$

Total time, $T_{1} + T_{2}$ = $4$ + $0.25$
$\Rightarrow T o t a l t i m e = 4.25 s e c o n d s$

Suggest Corrections

Similar questions

If a person drops a pebble in a well of $100 m$ depth, after how much time (in seconds) will he be able to hear the sound?
Given:
Acceleration due to gravity, $g = 10 m s^{- 2}$
Speed of sound in air, $v = 343 m s^{- 1}$

Tinku dropped a stone into a very deep well. He hears the sound $6.53 s$ after he dropped the stone. Find the depth of the well. Take acceleration due to gravity, $g = 10 m s^{- 2}$ and $v_{s o u n d} = 340 m s^{- 1}$ .

If a person drops a pebble in a well of $100 m$ depth, after how much time will he be able to hear the sound, starting from the time he drops the pebble? (Take $g = 10 m / s^{2}$ and speed of sound $= 343 m / s$ )

Tinku dropped a stone into a very deep well. He hears the sound 6.53 s after he dropped the stone. Find the depth of the well. Take acceleration due to gravity, g =10 $m s^{- 2}$ and $v_{s o u n d}$ = 340 $m s^{- 1}$ .

Join BYJU'S Learning Program

Sam was pulling water from a well of depth 80 m, when the key from his pocket fell into it. After how much time he would hear the sound of the metal key falling. Take speed of sound is 320 ms−1 and g =10 ms−2.

Sam was pulling water from a well of depth 80 m, when the key from his pocket fell into it. After how much time he would hear the sound of the metal key falling.
Take speed of sound is 320 ms $^{- 1}$ and g =10 ms $^{- 2}$ .