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Homework Help: Equation for mass

  1. Dec 4, 2005 #1
    what is the equation for mass when calculating its energy equivalent? For one gram of mass E = mc(squared) would be

    E = m * ( 9*10 to the 16th meters per second squared)

    what are the values I put in for m being 1 gram such that the end result will be energy. I have googled this but get all kinds of nonsense other that I want.

  2. jcsd
  3. Dec 5, 2005 #2


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    In the equation:

    [tex]E = mc^2[/tex]

    E is in Joules, m is in kilograms, and c is the speed of light in meters per second (~300,000,000 meters/sec).
  4. Dec 5, 2005 #3
    I understand the mass is in kilograms (1000 grams) but what is the exact expression I put in to the equation to get this thing to work out to the right units for energy:

    E = m * ( 9*10 to the 16th meters per second squared)

    for 1 kilogram, what is the full text to be used for replacing m?

    E = (1 kilogram) * ( 9*10 to the 16th meters per second squared)
    I just don't get this to work out to the right units.

    Thank you
  5. Dec 5, 2005 #4


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    If we check out the dimensions on the rhs of the eqn, mc², we get

    [kg][m²/s²] = [kg.m/s²][m] = [N][m] = [J]

    where we used units of kg for the mass and m/s for the speed.
    We end up with the units/dimensions of mc² being equivalent to Joules, which is work done or energy.

    So, if the mass that you are interestred in is, m = 1 kg, then the energy of this mass is,

    E = mc²
    E = 1[kg]*(3*10^8)²[m²/s²]
    E = 9*10^16 [kg.m/s²][m]
    E = 9*10^16 [J]

    Hmm, just noticed. You have the speed squared as metres per second squared. That should have been metres squared per second squared.
  6. Dec 5, 2005 #5
    I think I understand what you are saying. It seems I was putting too much into the definition of a (kilo)gram. So to put this in other words, if we could translate one kilogram of mass into its energy equivalent, we could get 9 * 10^16 watt seconds of electric power. Thats a lot of power.

    Yes, I did forget that meters squared.

    Thanks for your help.
  7. Dec 5, 2005 #6


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    I would just say, watt seconds of power. I don't think you need to specify it as electric.

    And yes, you do get a lot of power when you convert mass to energy.
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