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?

29

6.4

5.0

8.0

Answer 1

To find when the object will hit the ground, we need to find when h = 0.

So, we have:
-16t^2 + 64t + 80 = 0

Divide by -16:
t^2 - 4t -5 = 0

Factor the quadratic equation:
(t-5)(t+1) = 0

So, t = 5 or t = -1

Since time cannot be negative, the object will hit the ground after 5 seconds.

Therefore, the correct answer is 5.0 seconds.