1. The problem statement, all variables and given/known data The Moon and Earth have masses of 7.4 × 1022 kg and 6.0 × 1024 kg, respectively, and the distance between their centers is 3.8 × 108 m. The amount of work required to pull them further apart so that their separation increases by a factor of 1.6 is most nearly 2. Relevant equations Etot = -GMm/(2r) W=ΔE 3. The attempt at a solution ΔE=(-GMm/2)(1/(1.6*3.8 x 108) - (1/3.8 x 108)) = 1.44 x 1028 J Answer key says 2.9 x 1028 J That's twice my answer. Is it possible that the person who made the answer key forgot to factor out the /2. Or should I be considering only ΔU? I did a similar problem from this chapter using ΔEtot and got the right answer. What am I missing? Thanks!