# Total potential energy due to gravitational and electrostatic potential energy

 P: 104 1. The problem statement, all variables and given/known data Two dust particles are separated by 0.01m and of the same mass and charge, find the total potential energy 2. Relevant equations $$E_{el}=k\frac{q_1 q_2}{r}$$ $$E_{grav}=-G\frac{m_1 m_2}{r}$$ $$r=0.01 m$$, $$q_1=q_2=1.1201\times10^{-18} C$$ $$m_1=m_2=13\times10^{-9} kg$$ Where G and k are the gravitational and Coulomb's constant respectively. 3. The attempt at a solution $$E_{el}=1.128\times10^{-24} J$$ $$E_{grav}=-1.128\times10^{-24} J$$ Not sure whether it $$E_{tot}=E_{el}+E_{grav}$$ or $$E_{tot}=\left|E_{el}\right|+\left|E_{grav}\right|$$?
 P: 104 Well I have found the electrostatic and gravitational potential energies $$E_{el}=1.128\times10^{-24} J$$ and $$E_{grav}=-1.128\times10^{-24} J$$ Is it not their sum? I'm taking $$r=0$$ as the particles being together and $$E_{pot}=0$$ at $$r=\infty$$