math equation help

Question

if an object is thrown straight up from the top of a 210 foot tall building at 88 feet per second, the height of the object ater t seconds can be modeled by the equation h(t)= -16t^2+88+210. How long until the object hits the ground?

Answer 1

-16t^2+88t+210

complete the square

-16(t^2 - 11t/2+ 121/16) + 121+210

-16(t-11/4)^2 +331

in 11/4 = 2 3/4 seconds it reaches max h = 331 feet

over twice that time to reach the ground

-16t^2 +88t +210=0

-8t^2+44t +105=0

use the quadratic formula

t= 44/16 +/-(1/16)sqr(44^2+32(105))

=about 2.75 +4.55 = 7.3 seconds to hit the ground