Respuesta :
Answer:
D. 6 seconds.
Step-by-step explanation:
When the ball hits the ground f(t) = 0 , so:
-1/2t^2 + 2t + 6 = 0
Take out the -1/2:
-1/2(t^2 - 4t - 12) = 0
-1/2(t - 6)(t + 2) = 0
t = -2 , 6. We ignore the negative zero.
So the answer is 6 seconds.