Also, there's no reason to assume damage is directly proportional to kinetic energy. For instance, some quick research suggests that a musketball might have had about 809 ft/s muzzle velocity (which, for the sake of simplicity, let us assume is not subject to air resistance). The DMG's Renaissance weapons suggests that a musket ball would weigh .2 pounds; converting that to mass and then all the units to metric, (246.5 m/s)^2*.0907 kg = 5111 J. Now, a dagger weighs 5 times as much, and deals a bit less than 2/5 as much damage, on average. Thus, were damage a direct product of kinetic energy, we would expect a dagger to have 2044.4 J of energy, and thus a velocity of root(2044.4/.453) m/s, or 67.18 m/s; further research suggests that thrown knives move at around 14 m/s. I don't think that any reasonable margin of error accounts for this difference.