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+64t+80. How many seconds will it take to reach

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+64t+80. How many seconds will it take to reach       Log On


   

Question 98771: 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+64t+80. How many seconds will it take to reach ground level?
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
it reaches the ground when s=0 ... 0=-16t^2+64t+80 ... dividing by -16 gives 0=t^2-4t-5

factoring gives 0=(t-5)(t+1) ... so t=5 and t=-1 ... the negative value is not realistic