SOLUTION: Please help me solve this problem An object is projected upward from the top of the tower. it's distance in feet above the ground after t seconds is given by s(f)=-16t^2 +64t +

Question 71246: Please help me solve this problem
An object is projected upward from the top of the tower. it's distance in feet above the ground after t seconds is given by s(f)=-16t^2 +64t +80. How many seconds will it take to reach ground level?
I would really like to know how to figure this out.
Thanks to anyone who is willing to help me
Answer by Earlsdon(6294) (Show Source): You can put this solution on YOUR website!
After t seconds, the height of an object with an initial upward velocity of feet per second and an initial height of feet is given by the function:
In your problem, ft/sec and ft, so you have:

You want to know at what time, t, will the height, h, be 0, so set the function s(t) = 0 and solve for t.
You can simplify this a bit by factoring out -16.
so:
You can factor this quadratic equation.
Apply the zero product principle.
and/or
If then Discard this solution as the time must be a positive value.
If then
So the object will reach ground-level (h=0) in 5 seconds.

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