Question

An object is thrown upward from the top of an 80ft tower. The height h of the object after t seconds is represented by the quadratic equation h=-16t^2+64t+80. After how many seconds will the object hit the ground?

a)29 seconds
b)6.4 seconds
c) 5.0 seconds
d) 8.0 seconds

Answer 1

0 = -16t²+64t+80

Finding the roots of the equation:

-16(t² - 4t - 5) = 0

-16(t-5)(t+1) = 0

t = 5, t = -1. Time cannot be negative, so after 5 seconds it will hit the ground.