Energy released by a comet impact

Comet Shoemaker-Levy, which struck the planet Jupiter in 1994, had a mass of roughly 4 × 10¹³ kg, and was moving at a speed of 60 km/s. Compare the kinetic energy released in the impact to the total energy in the world's nuclear arsenals, which is 2 × 10¹⁹ J. Assume for the sake of simplicity that Jupiter was at rest.

Since we assume Jupiter was at rest, we can imagine that the comet stopped completely on impact, and 100% of its kinetic energy was converted to heat and sound. We first convert the speed to mks units, v = 6×10⁴ m/s, and then plug in to the equation to find that the comet's kinetic energy was roughly 7 × 10²² J, or about 3000 times the energy in the world's nuclear arsenals.