How many gigatons is it if a giant battleship slams into you?
So I know this was a rhetorical question, but I got curious about this, so I crunched the numbers just for laughs. This is an almost literal back-of-the-envelope calculation and subject to error, but here's what I came up with:
According to our ever-infallible friend Wikipedia, the official displacement of the battleship Musashi, fully loaded, was 74,000 metric tons, or 74 million kilograms. Her top speed is listed as an arrestingly specific 50.86 kilometers per hour, or 14.13 meters per second.
The kinetic energy of a body in non-circular motion is 1/2(mv^2); therefore, the kinetic energy of a fully-loaded Musashi at full speed is (7.4x10^7 kg * (14.13 m/s)^2)/2, or 1.477x10^10 joules - near as makes no difference, at that scale, call it 15 megajoules.
Now, that's a lot of energy. Even though the energy transfer in a collision would be nowhere near 100% efficient, you sure wouldn't want it to hit you in the face. But, alas, it's nowhere near a gigaton; a gigaton (TNT equivalent) is 4.184 exajoules (that's 4.184x10^18 joules), which in the old system of measurement is one point four million Imperial craploads.
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