What is the minimum speed with which a meteor strikes the top of Earth's stratosphere (about 43.5 km above the surface), assuming that the meteor begins as a bit of interplanetary debris far from Earth and stationary relative to Earth? Assume that the drag force is negligible until the meteor reaches the stratosphere. Mass of Earth is 5.974 * 10-4 kg; radius of Earth is 6.371 x 10 m; and gravitational constant is 6.674 x 10-11 N-m2/kg2. km/s