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A stone was dropped from the top of a building 40m high. Fin...

A stone was dropped from the top of a building 40m high. Find, correct to one decimal place, the time it took the stone to reach the ground. [Take g = 9.8ms2]

A.

2.9.seconds

B.

2.8 seconds

C.

2.6 seconds

D.

1.4 seconds

Correct answer is A

s = 12gt2 

40 = 12×9.8×t2

809.8=t2

t = 8.16326

t  2.9 secs