1. The problem statement, all variables and given/known data What is more likely to cause greater injury, a collision with a light person at fast speed or a person with twice the mass at half the velocity? 2. Relevant equations momentum = mv KE = 1/2mv^2 3. The attempt at a solution I am having a little trouble at which is appropriate here. I know momentum will be the same regardless, so if you are hit by either person you should travel backwards at the same velocity (your mass does not change)? Where as the other hand the lighter person has more kinetic energy, so do they pack a harder initial punch so to speak? I am more interested in understanding the difference between momentum and KE during a collision? Thanks everyone.