1. The problem statement, all variables and given/known data You run a race with your friend. At first you each have the same kinetic energy, but then you find that she is beating you. When you increase your speed by 21%, you are running at the same speed she is. If your mass is 77 kg, what is her mass? 2. Relevant equations K=1/2mv^2 3. The attempt at a solution K(initial me)=1/2*77*.79v K(initial friend)=1/2*mass*v 1/2*77*.79v=1/2*mass*v the v's cancel out so the mass should be 30.415/.5 or 60.83 but this is not the right answer. Does anyone know what I did wrong?