1. The problem statement, all variables and given/known data 4He2 has size of ~ 2 x 10^-15 m and a mass of 4.0015u. Calculate the binding energy of this nucleus, and compare it to the electrostatic repulsion of its constituents. 2. Relevant equations 3. The attempt at a solution For the first part I have calculated B.E. = 4.5 x 10^-12 J This agrees with my notes. For the second part do I use the equation E = (q1 x q2) / [4∏(ε0)r^2] Which would be; (1.6 x 10^-19)^2 / [4∏ x 8.85 x 10^-12 x (1 x 10^-15)^2] = 230 J The reason I ask is because in the notes I have the r = 1 x 10^-15 value is not squared in the same calculation therefore giving an answer of 2.3 x 10^-13 J. So I wasn't sure which is correct. Thanks for any advice!