SOLUTION: Hello, It's been awhile since I asked this question. I have not gotten any response yet. If a paper plane is thrown from the top of an 147ft cliff into water,the height of the

Question 907494: Hello,
It's been awhile since I asked this question. I have not gotten any response yet.
If a paper plane is thrown from the top of an 147ft cliff into water,the height of the plane at any given time can be determined by h = -3t^2 + 147, where h is the height of plane at t seconds. After how many seconds will the plane be at height of 20.25ft?
I have h = 3t^2 + 147
h(t) = 3^2 + 147 - 20.25ft
147 = 3t^2 = 6t = 147
0 = 3t^2 + 6t
Found 2 solutions by ewatrrr, richwmiller:
Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!
h = -3t^2 + 147
20.25 = -3t^2 + 147
t^2 = (147-2.025)/3
t =
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
h = -3t^2 + 147
-3t^2 is a very rough approximation of the acceleration due to gravity
20.25ft = -3t^2 + 147
In each step that you took you changed an important element of the equation.
h = 3t^2 + 147 here you changed gravity to a positive force making the paper plane rise and never fall
h(t) = 3^2 + 147 - 20.25 ft here you left out the time
h(t) is the height
so plug in the 20.25 ft here
20.25 = -3t^2 + 147
-126.75= -3t^2
42.25 =t^2
6.5=t
So after 6.5 second the plane is at 20.25 ft
This is assuming that a breeze doesn't catch it and take it away
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