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Question

A stone is dropped from the top of a tower of 500 m height, into a pond of water at the base of the tower. When is the splash heard at the top?

(Given g=10 ms2 and speed of sound =340 ms1)

A
10 s
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B
11.47 s
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C
1.10 s
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D
20 s
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Solution

The correct option is B 11.47 s
Given h=500 m , g=10 m/s2 , v=340 m/s,
Since the stone is under free fall, we can use the kinematic formula, h=12 gt2.
From the data given in the question,

500=12×10×t2
t2=1000/10t=10 s

It is the time taken by stone to reach the water level. After that, sound is produced due to the stone striking the water surface, and the sound travels upwards.

Let t be the time taken by the sound to reach the top of the tower.
Then, t=hv=500340=1.47 s

Therefore, total time taken for the splash to heard at the top,
T=t+t=10+1.47=11.47 s

Thus, option (b) is the correct answer.

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