SOLUTION: if an object is thrown upward with an initial velocity of 64 feet per second from a height of 80 feet, then the height in feet t seconds after it is thrown is given by the function

Question 131219: if an object is thrown upward with an initial velocity of 64 feet per second from a height of 80 feet, then the height in feet t seconds after it is thrown is given by the function f(t)=-16t^2+64t+80
how long after it is thrown will it hit the ground?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
f(t)=-16t^2+64t+80
how long after it is thrown will it hit the ground?
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When it hits the ground f(t) will be zero.
-16t^2+64t+80= 0
Solve for "t":
-16(t^2-4t-5)=0
Divide thru by -16 to get:
t^2-4t-5 = 0
Factor:
(t-5)(t+1) = 0
Positive answer:
t = 5 seconds.
The object will be on the ground in 5 seconds.
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Cheers,
Stan H.
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