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The Nucleus and Radioactivity

  1. Oct 15, 2015 #1
    1. The problem statement, all variables and given/known data
    I have the question with a diagram posted in the thumbnail to make things easier.

    2. Relevant equations
    E = mc²

    3. The attempt at a solution
    The homework only had a single example for a question like this so im not 100% sure how to get the answer. So far I've added the 2 masses:
    5.030151g and 5.011267g

    Then I subtracted them both 5.030151 – 5.011267 = 0.018884g

    Here is where im stuck. I know that from the example I need to do something like 1.8884 * 10^(input some number here) but I have no clue how to get the number that it should be to the power to. All I know is after this I need to multiply 1.8884 * 10 ^ (???) by 3.8 * 10 ^ 8 to calculate the total amount of energy produced using E = mc²
     

    Attached Files:

  2. jcsd
  3. Oct 15, 2015 #2

    SteamKing

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    Why are you assuming that the masses of the elements reacting are not in grams?

    I think you are assuming, based on the wording of the question, that only 1 atom of D and T react, but that need not be the case. Only the ratios of the reactants matter.

    Also, units should be carefully scrutinized here. If you take c in m/s, what mass units must you use in order to calculate energy in joules?
     
  4. Oct 15, 2015 #3
    Im not quite sure what you mean by all of that. I assume you mean I need to convert grams to a different unit of measurement but im not sure what. Also what do you mean by
    "I think you are assuming, based on the wording of the question, that only 1 atom of D and T react?"
     
  5. Oct 15, 2015 #4

    SteamKing

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    Well, joules are the SI units of energy. Joules are also derived units. What is the definition of a joule?

    https://en.wikipedia.org/wiki/Joule

    It's obvious that 1 atom of deuterium does not have a mass of 2.014102 g, but a certain number of deuterium atoms does have this total mass. Ever heard of a fellow by the name of Avogadro?

    https://en.wikipedia.org/wiki/Avogadro_constant

    If you're going to study physics, you've got to study units and understand how units are useful in deciphering physics problems.
     
  6. Oct 15, 2015 #5
    Ahh I see where I went wrong. The example
     
  7. Oct 15, 2015 #6
    Ahh I see where I went wrong. The example questions like to use numbers like 1.9 * 10^-4 rather than use the actual whole number so I got confused.

    I would need to convert grams to kilograms which would mean the number would now become: 1.8884 * 10^-5
    Now I plug it into E = mc^2 and get:

    E = 1.8884 * 10^-5 * (3 * 10^8)^2
    E = 1.7 * 10 ^ 12 (rounded of course)

    Im assuming this is the correct answer now?
     
  8. Oct 15, 2015 #7

    SteamKing

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    Always include the units in your calculation results. That's a habit you should acquire now.
     
  9. Oct 15, 2015 #8
    Ahh yes it would be in Joules...Thanks for the help!
     
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