well, first of all, what version do you have. Because if you own commercial, you can only have 1 physics object active at a time, which means that arrow would be the only object in your level, at that time, that would employ physics. With Newton, you can have unlimited, as I understand it. Preformance wise, from what I have read, they are about the same. You could use the laws of projectile motion to write your own physics , but that may be a little more trouble than its worth. Anyways, thats about the extent of my knowledge on physics, good luck.