Question 84101
An object is projected directly upward from the ground. After t secconds. the distance (s) from the ground is given by the equation: s=144t- 16t^2  . After how many seconds will the object reach 324 feet above the ground?
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s is the distance above the ground; so let s = 324 and solve for t.
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-16t^2+144t = 324
16t^2-144t+324 = 0
4(4t^2-36t+81) = 0
(2t-9)^2 = 0 
t = 9/2 or 4.5 seconds
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Cheers,
Stan H.