A stone is dropped into a 200m deep well, if the well is dry, after how much time the sound of stone hitting the bottom will be heared.
(speed of sound in air =340m/s and g=10m/s2)
A
6.91s
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B
8.52s
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C
11.43s
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D
2.51s
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Solution
The correct option is A6.91s
Depth of the well, h=200m
Speed of sound, v=340m/s
Let time taken by stone to reach the bottom of the well be t1, so, we have s=ut1+12at21 ⇒200=0+12×10×t21[∵s=h,u=0anda=g] ⇒t1=2√10=6.32s
Now, time taken by sound to reach the mouth of the well t2=hv t2=200340=1017s=0.59s
Time after which sound is heard is t=t1+t2=6.91s