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It gains ... and loses 3.738 x 10^18 joules of kinetic energy due to the slowing of its orbital speed. That assumes I didn't make any kind of calculation error.
I found an equation that predicted orbital velocity based on the distance a satellite is from a planet and the planet's mass. The equation is: orbital velocity (m/s) = square root ((gravitational constant x mass of the planet (kg)) / orbital radius (m)).The orbital velocity I calculated for the Moon's semi-major axis of 384,399,000 meters was 1,018.20824493 meters per second. Then I used Newton's kinetic energy equation to calculate how much kinetic energy the Moon (with a mass of 7.342 x 10^22 kilograms) would have at that velocity. The equation is: kinetic energy (J) = 0.5 x mass (kg) x (velocity (m/s))^2. The result was 38,059,020,182,894,347,263,576,879,000 joules.Then I repeated the calculations with the Moon being 3.82 centimeters further out (384,399,000.0382 meters), resulting in an orbital velocity of 1,018.20824488 meters per second and a kinetic energy of 38,059,020,179,156,504,796,530,624,000 joules. I subtracted the two to get a kinetic energy decrease of 3,737,842,467,046,255,000 joules per year.
There's an easier way. The total orbital energy can be found by:E= -GMm/2awhere a is the semimajor axis. By using 3.987e14 for GM (we actually know this product more accurately than we know either G or the mass of the Earth) and calling it U, you can find the energy difference by-Um/2 (1/a1-1/a2)For your given Moon mass, this works out to 3,783,812,701,003,630,000 Joules.
I think this video answers the question pretty nicely.