A stone is dropped from a certain height which can reach the ground in 5s. If the stone is stopped after 3s of its fall and then allowed to fall again, then the time taken by the stone to reach the ground for the remaining distance is
A
2s
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B
3s
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C
4s
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D
8s
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Solution
The correct option is B4s Let h be the height, t=5s ∴h=12gt2=12(9.8)(25)=122.5m Distance covered in 3sec=12(9.8)(3)2 =44.1m Remaining distance =122.5−44.1=78.4m If ts is the required time, then 78.4=0+12gt2 ⇒t2=78449=16 ⇒t=4s.