SOLUTION: An object is projected upward from the top of a tower. Its distance in feet above the ground after (t)seconds is given by s(t)= -16t^2+64t+80. How many seconds will it take to rea

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: An object is projected upward from the top of a tower. Its distance in feet above the ground after (t)seconds is given by s(t)= -16t^2+64t+80. How many seconds will it take to rea      Log On


   

Question 82299: An object is projected upward from the top of a tower. Its distance in feet above the ground after (t)seconds is given by s(t)= -16t^2+64t+80. How many seconds will it take to reach ground level? The answer is multiple choice.
a. 1 second
b. 4 seconds
c. 5 seconds
d. 8 seconds
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
s(t)= -16t^2+64t+80
When the ball is at ground-level s = 0.
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EQUATION:
-16t^2+64t+80 = 0
-16(t^2-4t-5)=0
t^2-4t-5=0
(t-5)(t+1)=0
Positive answer: t=5 seconds
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Cheers,
Stan H.