SOLUTION: The height h in feet of an object thrown upward from a height of 5 feet, with an initial velocity of 30 feet per second, is given by the equation h=-16t^2+30t+5, where h represents

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Question 916626: The height h in feet of an object thrown upward from a height of 5 feet, with an initial velocity of 30 feet per second, is given by the equation h=-16t^2+30t+5, where h represents the height of the object after t seconds. How long will it take the object to hit the ground?
Found 2 solutions by Alan3354, josmiceli:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
h=-16t^2+30t+5
---------
When it hits the ground, h = 0
h=-16t^2+30t+5 = 0
Solve for t

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+h+=+-16t%5E2+%2B+30t+%2B+5+
When the object hits the ground, the
height above ground = zero, so
+h+=+0+
+-16t%5E2+%2B+30t+%2B+5+=+0+
Solve using the quadratic formula
+h+=+%28+-b+%2B-+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29%29+%2F+%282%2Aa%29+
+a+=+-16+
+b+=+30+
+c+=+5+
+t+=+%28+-30+%2B-+sqrt%28+30%5E2+-+4%2A%28-16%29%2A5+%29%29+%2F+%282%2A%28-16%29%29+
+t+=+%28+-30+%2B-+sqrt%28+900+%2B+320+%29%29+%2F+%28-32%29%29+
+t+=+%28+-30+%2B-+sqrt%28+1220+%29%29+%2F+%28-32%29%29+
+t+=+%28+-30+-+34.928%29+%2F+%28-32%29%29+
( The positive root does not work here )
+t+=+%28+-64.928+%29+%2F+%28+-32+%29+
+t+=+2.029+
The object hits the ground in 2.029 sec
Here's the plot:
+graph%28+400%2C+400%2C+-1%2C+3%2C+-2%2C+20%2C+-16x%5E2+%2B+30x+%2B+5+%29+