Alright I will throw in my opinion. Both KE and Momentum (p) have there place in physics. When attempting to estimate the penetration power, so to speak, of your arrow I think "p" might be a better route. p is basically a way of measuring inertia, since inertia is a principle and can't be measured directly (p is most comprable). Inertia is a principle which states an object will remain at a current state untill acted on by an outside force. It something is sitting still, it will continue to do so until acted on be a force. If something is moving, it will continue to do so until acted on by an outside force. This pertains to a flying arrow. How much inertia (momentum) an arrow has dictates how much force is required to stop it.

P.S. THis is downscaled to be more easily understood. Everthing is reletive; however not 100% correct. Inertia and p are not interchangable, but for practical purposes...


[8D]