Answer:
Step-by-step explanation:
Start with h(t) = -16t^2 + initial height, which here is h(t) = -16t^2 + 1296. Set this = to zero, which corresponds to the object hitting the ground (h = 0):
0 = -16t^2 + 1296. Dividing all terms by -16, we get t^2 = 81, whose positive square root is 9. It takes 9 seconds for the object to hit the ground.
