3 in diameter rod, 3 feet long. Volume is pi-rsquared times length. 3.1415 * (1.5^2) * (3*12) gives 254.5 cubic inches. Times (2.54 ^ 2) to convert to cubic centimeters, times 19.25 (density of tungsten in grams per cc) to give mass in grams, divide by 1000 gives mass in kilograms: 31.6 kg, about 65 pounds.
Above someone says that they're moving about Mach 10 by the time they hit the ground. That makes sense, orbital speed is Mach 25, but they'll lose a lot of that by the time they get through the atmosphere.
1/2 * m * v^2 = 1/2 * 31.6 * ((343 meters/sec * 10)^2) = 185,885,420 joules of energy. Convert joules to kilotons by multiplying by 2.4 x 10^-13. 1.85885420x10^8 * 2.4x10^-13 gives 4.46x10^-5 or 0.0000446 kilotons, quite a bit less than 12.
You know, when people say “do the math”, they generally don’t expect that anyone will actually do the math.
;)
Using the equation for terminal velocity, integrating the pull of gravity and air density, and using a Cd around 0.0006 (about what a thin, guided rod would have - typical for an arrow) I get a terminal velocity that is really high - around 31,000 meters per second. Is that reasonable? Well, there is essentially zero cross section, a lot of mass, zero drag, low air density for most of the flight, and lots of distance for gravity to work over...
Sanity check: most meteorites strike around 17,000 m/s so given we're quite a bit more aerodynamic than a meteorite, it's not all that unbelievable.
One kiloton of TNT is about 4.2 gigajoules, which is a lot smaller than your number (which seems to be about 1000 times too high). Run it all, and you're around 11-12 kilotons of energy.
Unless I'm off somewhere!
Rod from God are not Earth launched ballistic objects. They launch from space platforms and can achieve far greater speeds than Mach 25.