The Physics
Opus in profectus


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  1. Hydrogen fusion in the sun is a multistep reaction, but the net result is that four hydrogen atoms fuse into one helium atom (plus a bunch of junk).

    411H → 42He + 2(0+1e + 00γ + 00ν)

    The mass of the sun is 1.99 × 1030 kg, 91% of which is hydrogen. Its power output is 3.85 × 1026 W. Determine…

    1. the mass of four hydrogen atoms
    2. the mass defect when four hydrogen atoms fuse into one helium atom (in atomic mass units and megaelectronvolts)
    3. the rate at which the sun's mass is decreasing
    4. the total mass destroyed if all the sun's hydrogen were converted into helium
    5. the expected lifetime of the sun (assuming its power output will remain constant)
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  1. problem