Great you got it working! The impulse and force are actually different units and applied differently by the physics engine. The force will be applied during the course of the time step, which is why you need to divide the impulse by the time step, roughly equivalent to * 60. More discussion about that in the Box2d forum.
Sorry, but it’s not possible to change the mass and radius at runtime. Mass is problematic because how it’s usually derived from shapes and densities. Radius is tricky because we have not yet decided on a good API to access things below the component level (collision object > collision shape in this case). Unless there is a popular request to do this, they would unfortunately get a low priority.
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