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Math Help - Mass and Energy Problems

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    Mass and Energy Problems

    If an electron and it positron (antielectron), each with a rest mass of 9.11 x 10^-31 kg, met and annihilated each other, how much radiant energy would be produced? (In such a reaction involving matter and antimatter, the mass is completely converted into energy in the form of gamma rays.) Assume that the particles were barely moving before the reaction.

    Answer:1.64 x 10^-13 J


    The Sun radiates away energy at a rate of 3.9 x 10^26 W. At what rate is it losing mass due to this radiation?

    Answer: 4.3 x 10^9 kg/s
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    Quote Originally Posted by kenan View Post
    If an electron and it positron (antielectron), each with a rest mass of 9.11 x 10^-31 kg, met and annihilated each other, how much radiant energy would be produced? (In such a reaction involving matter and antimatter, the mass is completely converted into energy in the form of gamma rays.) Assume that the particles were barely moving before the reaction.

    Answer:1.64 x 10^-13 J


    The Sun radiates away energy at a rate of 3.9 x 10^26 W. At what rate is it losing mass due to this radiation?

    Answer: 4.3 x 10^9 kg/s
    Both of these answers are basically E = mc^2.

    For the electron-positron collision you need to know that the mass of a positron is the same as the mass of an electron.

    For the Sun problem, P = \frac{\Delta E}{\Delta t}

    = \frac{\Delta (mc^2)}{\Delta t} = c^2 \frac{\Delta m}{\Delta t}

    You are looking for \frac{\Delta m}{\Delta t}

    -Dan

    -Dan
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