SOLUTION: The height h in feet of an object after t seconds is given by the function h = –16t^2 + 90t + 3. How long will it take the object to hit the ground? Round your answer to the

Algebra ->  Quadratic Equations and Parabolas -> SOLUTION: The height h in feet of an object after t seconds is given by the function h = –16t^2 + 90t + 3. How long will it take the object to hit the ground? Round your answer to the      Log On


   

Question 89492: The height h in feet of an object after t seconds is given by the function
h = –16t^2 + 90t + 3.
How long will it take the object to hit the ground? Round your answer to the nearest thousandth, and explain which solution is the correct one.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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The height h in feet of an object after t seconds is given by the function
h = –16t^2 + 90t + 3.
How long will it take the object to hit the ground? Round your answer to the nearest thousandth, and explain which solution is the correct one.
:
When the object strikes the ground, h = 0, so we have:
-16t^2 + 90t + 3 = 0
:
A quadratic equation, that requires the quadratic formula to solve:
a = -16, b = 90, c = 3
:
t+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
:
t+=+%28-90+%2B-+sqrt%28+90%5E2+-+4+%2A+-16+%2A+3+%29%29%2F%282%2A-16%29+
:
t+=+%28-90+%2B-+sqrt%28+8100+-+%28-192%29+%29%29%2F%28-32%29+
:
t+=+%28-90+%2B-+sqrt%28+8100+%2B+192+%29%29%2F%28-32%29+; minus a minus is a plus
:
t+=+%28-90+%2B-+sqrt%28+8292+%29%29%2F%28-32%29+
:
Do the math here and you should get two solutions:
t = 5.658
and
t = -.033
:
Obviously, it cannot be a neg value when you are dealing with time of an event