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 reac

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Question 59420: 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?
Answer by funmath(2933) About Me  (Show Source):
You can put this solution on YOUR website!
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?
let s(t)=0 that's at ground level.
0=-16t%5E2%2B64t%2B80
0%2F-16=-16t%5E2%2F-16%2B64t%2F-16%2B80%2F-16
0=t%5E2-4t-5 factor
0=(t+1)(t-5)
t+1=0 and t-5=0
t+1-1=0-1 and t-5+5=0+5
t=-1 and t=5
Negative time is not valid.
Therefore highlight%28t=5s%29
Happy Calculating!!!