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propelled upward

by sanju09 » Fri May 14, 2010 1:55 am
If an object is propelled upward from ground level with an initial velocity of 224 feet per second, its height h in feet t seconds later is given by the equation h = 224 t - 16 t^2. After how many seconds does the object hit the ground?
(A) 0
(B) 4
(C) 14
(D) 24
(E) 54
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by jusgaurav » Fri May 14, 2010 2:04 am
Option C
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by nakul_anand » Fri May 14, 2010 2:42 am
So if the height is 0, then we get t=14 seconds from the equation.

But what's the logic behind selecting h as 0?
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by jusgaurav » Fri May 14, 2010 2:57 am
1. obviously, when object hits the ground, h would 'become' 0.
2. you can also notice that as value of t increases from 1 to 8, value of h increases to 768. as value of t becomes 9, value of h declines to 720, then 640 (@ t=10) until h becomes 0 at t=14.
I hope it resolves your query!
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by nakul_anand » Fri May 14, 2010 3:13 am
It sure does.

Thank you!
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