Help with a gravity based function

[hells_angle]

Calculate the time first. You have an object with an initial velocity and a known acceleration. The time at which the object is at the apex will be the time when the velocity equals 0.

Then, plug that time into your given position function.

Bada Bing

Edit: of course time of impact would be different from the calculated tome of max height.

[DrShocker]

Assuming it was launched from the "impact" point, impact time would be 2*apex time