Ummm... Mass should not be involved in most gravity equations. Rather, it should
, but in an earthlike situation it has an absolutely negligible effect, and all objects get accelerated by the gravitational constant.
Gravity is two objects with mass pulling on each other. In everyday life, we only notice the earth pulling on individual objects. That's because of this equation:
(force applied by gravity) = (mass of object 1) * (mass of object 2) * (coefficient of gravity) / (distance between objects squared)
Since acceleration applied to an object is (force applied) / (mass of object), gravitic acceleration (what we are interested in), is simply:
(acceleration from gravity) = (mass of other object) * (coefficient of gravity) / (distance between objects squared)
In planetary situations, we simplify the scenario by having a steady rate of gravitic acceleration. On earth, that's 9.84 m/s.So, in a game, just accelerate your objects by a steady rate. Leave mass out of it.
In summary: leave mass out of your gravity accelerations; it's useful for momentum and force equations instead.