Question 681777
If an object is projected vertically upward from an altitude of a feet with an initial velocity of v ft/sec, then its distance s(t) above the ground after t seconds is
s(t) = −16t2 + vt + a.
If s(1) = 99 and s(4) = 129, what are v and a? 
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Substitute and solve:
s(4) = -16*16 + 4v + a
129 = -256 + 4v + a
4v + a = 385
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s(1) = -16 + v + a
v + a = 99 + 16 = 115
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You have 2 equations:
4v + a = 385
v + a = 115
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Subtract and solve for "v":
3v = 270
v = 90
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Solve for "a" using v + a = 115
90 + a = 115
a = 25
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Cheers,
Stan H.
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