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Mass to energy equivalence question

  1. Dec 21, 2012 #1
    1. The problem statement, all variables and given/known data

    An unknown amount of mass lost from a fusion reaction is converted to energy. Determine the amount of mass equal to 17.6 MeV of energy.

    2. Relevant equations

    E=mc2?

    3. The attempt at a solution

    17.6=m(931.5)
    m=0.01889u
    Not sure if this is correct
     
  2. jcsd
  3. Dec 21, 2012 #2

    rude man

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    Where did "931.5" come from? √(931.5) = 30.52, I don't recognize this as being c ...
     
  4. Dec 21, 2012 #3

    Dick

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    931.5 MeV is the rest energy of 1 amu of mass. The 'attempt at a solution' wasn't very well explained. To say the least.
     
    Last edited: Dec 21, 2012
  5. Dec 21, 2012 #4

    rude man

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    Yeah, so looks like E = mc2 is irrelevant & we have just a ratio of energies and finding out how many gm to 1 a.m.u.?
     
  6. Dec 21, 2012 #5

    Dick

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    The easy way to solve it is to use 1amu*c^2=931.5 MeV (because you've memorized it) and solve it using ratios. That's how the OP got the right answer if u=amu. But the OP butchered the units and I know the OP doesn't know whether it's right or wrong. That's not good. Just using E=mc^2 and paying some attention to units would be much better. It would show understanding. It's hardly irrelevant. I was just pointing out where the 931.5 came from.
     
    Last edited: Dec 21, 2012
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