Question

a stone is dropped from top of a cliff It is seen to hit the ground below after 4.2 seconds .how high is the cllif​

Answer 1

Explanation:

$stone \: is \: dropped.... \\ \\ so...u = 0 \: \frac{m}{sec} \\ \\ t = 4.2 \: sec \\ \\ as \: t \: is \: free \: fall \: motion....a = g = 10 \frac{m}{ {sec}^{2} } \\ \\ h \: is \: unknown.... \\ \\ by \: 2nd \: kinematical \: eqution.... \\ h = ut - \frac{1}{2} (g {t}^{2} ) \\ \\ substiuting \: the \: vaues..... \\ \\ h = (0 \times t) - \frac{1}{2} (10)( {4.2}) ^{2} \\ \\ h = - 5 \times 17.64 \\ \\ h = 88.2 \: metres.....$

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