1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Homework Helper

    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


    User Avatar
    Homework Helper

    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


    User Avatar
    Homework Helper

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook