A stone dropped from the top of a tower travels 15m in the last second of its motion. If g=10ms−2 then the time of fall is
A
2s
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B
2.5s
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C
5s
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D
3s
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Solution
The correct option is A2s Let 'n' be the last second of travel s=u+a2(2n−1) (u is 0) 15=g2(2n−1) n=2 2nd second is the last second of travel. Therefore time taken to reach the bottom is 2.