@DRLeria I don’t think you need to try and calculate the effects of gravity, because the scene has gravity, and we know the imposter already has a mass, so if you do a getLinearVelocityToRef to get the y component from the current velocity before we modify it on key press, and just preserve that, the engine will do all the work of incrementing and decrementing based on our dampening etc.
I did exactly what you just did a few hours ago trying to figure this out 
great minds!