Answer:
3 seconds
Explanation:
h = -16t² + 48t
When h = 0, the height of the rocket is 0, so the rocket is on the ground.
0 = -16t² + 48t
Switch sides.
-16t² + 48t = 0
Factor the left side.
-16t(t - 3) = 0
-16t = 0 or t - 3 = 0
t = 0 or t = 3
The rocket is at zero height at t = 0 since that is the time that it is launched just before it lifts off the ground. Then it is again at zero height after 3 seconds because that is when it hits the ground after having been launched.
Answer: 3 seconds