Question

A stone falls from a rooftop in 2sec. If g=10m/sec2

, find the final

velocity of the stone and height from which it falls

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Answer 1

$h = ut + \frac{1}{2} g {t}^{2} \\ h \: = \frac{1}{2} 10 \times 4 \\ h = 20 \: m \\ \\ {v}^{2} - {u}^{2} =2gh \: \: \: \: \: (initially \: at \: rest\\ {v} = \sqrt{2gh} \\ v = \sqrt{2 \times 10 \times 20} \\ v = \sqrt{400} \\ v= 20 \: m {s}^{ - 1}$