SOLUTION: A ball falls off the top of a roof 320 feet above the ground. The formula h= -16t^2 + 16t +320 describes the height of the ball above the ground, h, in feet, t seconds after the f

Question 281657: A ball falls off the top of a roof 320 feet above the ground. The formula h= -16t^2 + 16t +320 describes the height of the ball above the ground, h, in feet, t seconds after the fall begins. How long will it take the ball to strike the ground.
Answer by Greenfinch(383) (Show Source): You can put this solution on YOUR website!
Ball hits ground when h = 0
So equation becomes 0= -16t^2 + 16t +320
Divide by -16 to get t^2 - t - 20 = 0
So (t-5)(t + 4)=0
t = 5 or -4 seconds
So t = 5
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