I understand the concept of angular momenum, but I do not understand how to use it in this problem: An asteroid of mass 1.0 * 10^5 kg, traveling at a speed of 30 km/s relative to the Earth, hits the Earth at the equator. It hits the Earth tangentially and in the direction of Earth's rotation. Use angular momentum to estimate the fractional change in the angular speed of the Earth as a result of the collision? First off, what is fractional change? I set up a conservation of momenum problem, momentum of Asteroid + momentum of Earth= momentum of Asteroid prime + momentum of Earth prime.