1. The problem statement, all variables and given/known data A mass of 3kg is 1m above the floor. the zero of the potential energy is chosen to be on the floor. I understand that the 30j potential energy belongs to both the earth and the mass, so, why don't i take into account also the distance to the center of the earth? Why don't i take the distance to the center of the earth as the potential energy? why is h1 better than h2 (see drawing)? What does the zero line mean? 2. Relevant equations ##E_P=mgh## 3. The attempt at a solution Is it related to the fact that only differences in potential energy count?