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Home Q & A Board Science-Related Homework Help Physics
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juan123 juan123
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11 years ago
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 = - 16t^2 ? 32 t + 128. How long will it take the ball to reach the ground?
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ikimikim
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11 years ago
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#2
11 years ago
This is probably Algebra II, quadratic equations.

Here's the equation:
S = - 16t^2 ? 32 t + 128

At time = zero, you get 128 feet. So, S is distance above the ground. So, the ball hits the ground when S=0.
0 = -16t² ? 32t + 128
Simplify the quadratic and factor:
0 = t² + 2t - 8 = (t + 4)(t - 2)

Now, for (t + 4)(t - 2) to be equal to zero, either 0 = t + 4 or 0 = t - 2
So, t=-4 or t = 2sec

+2 seconds is the one.
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