Homework Help: math

Posted by Anonymous on Friday, October 12, 2012 at 11:21pm.

an object is thrown upward from the top of a 80-foot building with a initial velocity of 65 feet per second. The height h of the object after t seconds is given by the equation h=-16t2+64t+80. when will the object hit the ground

math - Reiny, Saturday, October 13, 2012 at 7:24am
Your equation does not match your data

if the equation is
h = -16t^2 + 64t + 80 , then the initial velocity was 64 ft/sec, not 65 like you typed.
I will go with the 64

-16t^2 + 64t + 80 = 0
divide each term by -16
t^2 - 4t - 5 = 0
(t+1)(t-5) = 0
t = 5 or -1 , we will reject the last answer

the object will hit the ground after 5 seconds

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