So I saw someone post this question on facebook and naturally being an Engineering student I'm curious to know now. I haven't done any Physics in a while so I'm not sure how you would tackle this one. The question was: "The power needed to operate your body is about 120 watts. Suppose your mass is 60kg and your body could run on fusion power. If you could convert 0.8% of you mass into energy, how much energy would be available to run your body and for how long could you operate on fusion power?" My first instinct was to just take 0.8% of 60 kg to get .48 kg and plug that into the mass-energy equivalence equation to get E = (.48 kg)(3x1088 m/s)2 E = 4.32x1016 J then do 4.32x1016 J/120 Watts to get 3.6x1014 second. I'm not even sure if the mass-energy equivalence equation can be applied to this situation or not. I don't think there is a way to use the nuclear binding energy equations either, however I'm not a physicist and don't know nuclear physics too too well. Well thanks for any explanations.