SOLUTION: If a ball is thrown downwards from a height of 128 feet with an initial velocity of 32 feet per second and its height above the ground is given by the formula S = - 16t2 – 32 t + 1

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Question 209373: If a ball is thrown downwards from a height of 128 feet with an initial velocity of 32 feet per second and its height above the ground is given by the formula S = - 16t2 – 32 t + 128. How long will it take the ball to reach the ground?
Answer by nerdybill(7384) About Me  (Show Source):
You can put this solution on YOUR website!
Since 'S' is the "height above the ground", set it to zero and solve for t:
S = - 16t^2 – 32 t + 128
0 = - 16t^2 – 32 t + 128
Divide both sides by -16:
0 = t^2 + 2t - 8
Factoring the right:
0 = (t+4)(t-2)
t = {-4, 2}
We can throw out the negative solution leaving:
t = 2 seconds