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Homework Help: Relastivistic reaction?

  1. Aug 8, 2006 #1
    Old stars gets there energy from the fusion of 3 helium cores to one carbon-12 core. The resting mass of one carbon-12 is 2,99805 times bigger then the helium core. How much energy do you i from 1kg of helium? how do I even attack this problem?
     
    Last edited: Aug 8, 2006
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  3. Aug 8, 2006 #2

    Astronuc

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  4. Aug 8, 2006 #3

    HallsofIvy

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    Let m be the rest mass of one helium core. Then three helium cores have mass 3m but the resulting carbon-12 core has mass only 2.99805m. Energy has been released equivalent to (3- 2.99805)m= 0.00195m. Since that is for 3 helium cores, with 1 kg of helium, you can take the total m= 1/3 kg. Now use E= mc2.
     
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