I found there are a few problems when you do things such as set mass and change height/width of an object with physics movement...
When you set mass, the force of gravity and in fact, any forces you apply seem to decrease drastically...
The way I'm doing the movement is by applying forces to make the object move, but I wanted the object to be able to get larger as you played... But I discovered that it doesn't work well at all...
So, I decided, while that doesn't work, let's see if I can do some mass based gameplay then...
Unfortunately, increasing or decreasing the mass cause different problems... Interestingly, you cannot get the new value of the mass via the object's actions...
Here's a demo app of the problem with buttons to change parameters and a debug readout of what construct returns the mass as... Note what happens when the size of the ball is changed...
http://ssbfalcon.googlepages.com/physicsProblem.cap