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 = 9.8ms\(^{-2}\)]

  • A 2.9.seconds
  • B 2.8 seconds
  • C 2.6 seconds
  • D 1.4 seconds
waec 2020furthermathematics

The correct answer is A. 2.9.seconds

s = \(\frac{1}{2}gt^2\) 

40 = \(\frac{1}{2} \times 9.8 \times t^2\)

\(\frac{80}{9.8} = t^2\)

t = \(\sqrt{8.16326}\)

t ≈ 2.9 secs

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