I'm with NovaCoder on this, you're severely underestimating how complex this stuff is. I hate to be a big pessy, but I don't think you will ever see these kinds of games on an Amiga, it just doesn't have the CPU power for it.
I don't think it's valid to liken these physics to that of games like Worms or Pinball Dreams. Worms f.ex isn't something you just throw together, but frankly I think the physics of it is closer to plain animation than real time rigid body physics.
Also I don't think fixed point math will suffice. The problem is you have no dynamic range with fixed point math, and so you can have either big numbers or small numbers, but not both. You can always add more digits of course but it quickly becomes prohibitive in terms of performance. I think this is something you MUST use floating point math for.
For anyone curious of just how complex it is to simulate what happens when a couple of squares and circles bump into eachother, you can download the physics engine used in Angry Birds and have a look. It's called Box2D and is free and open source, you don't have to start from scratch or even know how it works, so the optimistic and diligent of you can compile it for Amiga and start porting Angry Birds right away