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 seconds
6.4 seconds
5.0 seconds
8.0 seconds

Answer 1

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

So, we set h = 0 in the equation:
0 = -16t^2 + 64t + 80

Rearranging the equation:
16t^2 - 64t - 80 = 0
Dividing the equation by 16:
t^2 - 4t - 5 = 0
(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