<PRE><B>Question 793319</B>
A ball is dropped from a building. The distance, D metres, that it falls in t seconds is given by

D=5t^2

a. Find the distance fallen in 3 seconds
Sub 3 for t
D = 5*3^2 = 45 meters

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B. Find the time to fall 100 metres
100 = 5t^2
t^2 = 20
t =~ 4.472 seconds
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