Solving a Gr. 11 Physics Assignment: Finding Vertical Displacement of a Potato

[Gombay]

I have to find the vertical displacement of a potato shot out of a potato launcher (Gr. 11 Physics assignment). It would make sense (and make this easier) to assume that the potato went straight up and down and I am allowed to assume that air resistance is negligible. My main problem is proving algebraically that the upward motion and downward motion are equal in terms of time. If they aren't equal I guess I need to start my thinking all over. Here are my givens if they are needed:
m = 249g
Δt = 4.15s

Any help would be appreciated. Thanks.

 

[rockerdoctor]

This problem is based around gravity. Think about how gravity affects the rate of any falling object. Also, remember the acceleration of gravity is a constant. So we can assume it will decelerate going up the same rate it accelerates falling back down, meaning the time it takes to go up=time it takes to fall (4.15s). We know that if we start at the top and let it fall the initial velocity is 0, the acceleration downwards is gravity or 9.8m/s^2, and we know it takes 4.15s to fall. If you have the right formula, those numbers will give you the answer. Think of the formula that incorporates constant acceleration, time, and displacement.