An object is projected directly upward from the ground After

An object is projected directly upward from the ground. After t seconds its distance in feet above the ground is s = 144t

Solution

a. After how many seconds will the object be 128 feet above the ground?
128 = 144t - 16t^2
-16t^2 + 144t - 128 = 0
-t^2 + 9t - 8 = 0
t = 3, 6
3 seconds going up
6 seconds coming down
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b. When does the object strike the ground?
144t - 16t^2 = 0
t = 0 (at launch)
t = 9 seconds (at impact)