Ok, here's the problem. I am evaluating multiple crossbows to predict the changes caused by various arrow weights. The original arrow mass and velocities are available. I input the two formula's: KE = 1/2MV^2 and MO = MV and solve for each, and then use those results with new arrow weights to solve for the new velocities. My problem is that I get different results. Which should prove to be the most accurate predictor and why? I know the results will not be pure because they don't include friction and other variables, but just based on the formula's above I was expecting closer results.