SOLUTION: The equation h = - 16t^2 + 40t + 5 gives the height in feet of a baseball as a function of time in seconds after it is hit. How long does it take for the baseball to hit the ground

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Question 1023093: The equation h = - 16t^2 + 40t + 5 gives the height in feet of a baseball as a function of time in seconds after it is hit. How long does it take for the baseball to hit the ground?
Found 2 solutions by robertb, ikleyn:
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Solve h%28t%29+=+-+16t%5E2+%2B+40t+%2B+5++=+0
==> t+=+%285%2B-sqrt%2830%29%29%2F4 by using the quadratic formula and simplifying.
Choose t+=+%285%2Bsqrt%2830%29%29%2F4+=+2.62seconds, to two decimal places (for obvious reasons.)

Answer by ikleyn(52767) About Me  (Show Source):
You can put this solution on YOUR website!
.
The equation h = - 16t^2 + 40t + 5 gives the height in feet of a baseball as a function of time in seconds after it is hit.
How long does it take for the baseball to hit the ground?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 

Assuming that the ground level is at h = 0 (you didn't say it in the condition), solve the equation 

-16t%5E2+%2B+40t+%2B+5 = 0

for t. Use the quadratic formula

t%5B1%2C2%5D = %28-40+%2B-+sqrt%2840%5E2+-+4%2A%28-16%29%2A5%29%29%2F%28-32%29%29 = %2840+%2B-+sqrt%2840%5E2+%2B+4%2A16%2A5%29%29%2F32 = %2840+%2B-+sqrt%281920%29%29%2F32 = %2840+%2B-+43.82%29%2F32.

You need the positive root t = %2840+%2B+43.82%29%2F32 = 2.6 seconds.

The problem is solved.