Question 171383
h=-1/4t^2+t+3
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When the ball hits the ground, the height is zero.
So, set h to 0 and solve for t:
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h=-1/4t^2+t+3
0 = -1/4t^2+t+3
multiply both sides by -4:
0 = t^2-4t-12
factoring:
0 = (t-6)(t+2)
t = {-2, 6}
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Tossing out the negative solution:
t = 6 seconds