1. The problem statement, all variables and given/known data Find the kinetic energy lost 2. Relevant equations 3. The attempt at a solution We solved it in class Ek1 = -206 J Ek2 = 10 J Find the energy lost. The answer is was 2.2 * 10^2 J lost This is confusing for me, to find energy lost, we should subtract the initial energy from the final energy, or should we subtract the final from the initial? So is the answer Ek1 - Ek2 = -206 J - 10 J = -216 J or Ek2 - Ek1 = 10 J - (-206 J) = 216 J How do we do it? I know for example if someone has say 10 marbles, and loses 3, we have seven left. So the amount lost should be 10 - 7 = 3 Or initial - final. Or is it final - initial = 7 - 10 = -3 ?