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Kinetic Energy Estimation.

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Posted by Alexander on January 9, 2002 19:53:31 UTC

Let's see, what is the K of 1000-ft asteroid. Assuming typical potato-shape with the average diameter 1000 ft (=about 0.3 km), its volume is about piD^3/6 = 1.4x10^7 m^3. If it is rocky asteroid (typical density D=3 g/cm^3), than its mass is about 4.2 x 10^10 kg, if iron-nickel (D=8 g/cm^3) then 1.1x10^11 kg.

Typical velocities of fly-by Earth asteroids are in 20-60 km/sec range. Let's take average 40 km/sec. Then the kinetic energy of 1000-ft rocky asteroid K =mv^2/2 is about 3.4x10^19 J and of the iron one - about 9x10^19 Joules.

How much is it anyway?

1 kiloton of TNT releases about 4x10^12 J, so average 20-KT atomic bomb (like Hiroshima one) releases about 8x10^13 J, and largest ever tested H bomb (russian 50-MT one) releases about 2x10^17 Joules.

Usually small 1 MT H bomb makes 1.2-mile diameter fireball, kills and levels practically everything within 8 mile diameter circle and makes major damages and lethally burns unprotected victims within 20 mile circle.

Asteroid impact of similar energy usually makes damages within factor 2-3 less radius than bomb, because it releases most energy underground.

Now, our rocky asteroid releases energy equivalent to about 8 Gigaton of TNT, which is about 0.4 millions Hiroshima bombs or 8 thousands small 1-Megaton H bombs, or about 160 large 50-MT H bombs.

Such amount of H bombs would produce fireball of about 40-mile diameter, levels and kills everything within 250 miles circle and makess essential damage within 700 mile circle.

Our Rock asteroid would make similar damages within 2-3 times smaller circle, and the iron one - within about 2 times more, killing everything within about 200 miles and essentially damaging everything within 600 miles.

This is indeed comparable to a small country.

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