# Thread: Mass and Energy Problems

1. ## 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.

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?

2. Originally Posted by kenan
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.

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?

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