SOLUTION: A girl stands on the edge of her dorm roof and throws a ball into the air. The ball's height above the ground after t seconds is given by h = -16t^2+16t+320 When will the ball hit

Question 1003154: A girl stands on the edge of her dorm roof and throws a ball into the air. The ball's height above the ground after t seconds is given by h = -16t^2+16t+320 When will the ball hit the ground?
Answer by rothauserc(4718) (Show Source): You can put this solution on YOUR website!
h = -16t^2+16t+320
we want to solve the quadratic for t when h = 0
-16t^2+16t+320 = 0
divide both sides of = by -16
t^2 -t - 20 = 0
now factor the quadratic
(t-5) * (t+4) = 0
we get two solutions for t, that is t = 5 or -4
we reject the -4 solution since time does not run backwards
t = 5 seconds is the solution,
the ball will hit the ground in 5 seconds

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