Chapter 12, Problem 48EAP

Impact Energies. A relatively small impact crater 20 kilometers in diameter could be made by a comet 2 kilometers in diameter traveling at 30 kilometers per second (30,000 m/s).

1. Assume that the comet has a total mass of  $4.2\times {10}^{12}$ kilograms. What is its total kinetic energy? (Hint: The kinetic energy is equal to  $\frac{1}{2}m{v}^2$, where m is the comet’s mass and v is its speed. If you use mass in kilograms and velocity in m/s, the answer for kinetic energy will have units of joules.)
2. Convert your answer from part a to an equivalent in megatons of TNT, the unit used for nuclear bombs. Comment on the degree of devastation the impact of such a comet could cause if it struck a populated region on Earth. (Hint: One megaton of TNT releases  $4.2\times {10}^{15}$ joules of energy.)