# Math Help - 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.

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

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.

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