SOLUTION: A particle is projected from ground level so that its height above the ground after " t " seconds is given by 20t - 5t^ m. After how many seconds is it 15 m above the ground? can y
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Question 682113: A particle is projected from ground level so that its height above the ground after " t " seconds is given by 20t - 5t^ m. After how many seconds is it 15 m above the ground? can you explain briefly why there are two possible answers? Answer by nerdybill(7384) (Show Source):
You can put this solution on YOUR website! A particle is projected from ground level so that its height above the ground after " t " seconds is given by 20t - 5t^ m. After how many seconds is it 15 m above the ground? can you explain briefly why there are two possible answers?
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height = 20t - 5t^2
set height to 15 and solve for t:
15 = 20t - 5t^2
3 = 4t - t^2
t^2 + 3 = 4t
t^2 - 4t + 3 = 0
factoring:
(t-1)(t-3) = 0
t = {1, 3}
t = 1 second and 3 seconds
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There are two answers because it reaches the height of 15 m on the way up and again on the way down.
