Recently, I gave my introductory physics course a fairly standard problem, based on the Matter and Interactions textbook. I've modified the question, but it goes something like this: You have a spacecraft with a mass of 100 kilograms, moving near Mars (the planet, not the candy bar). At one point, it is traveling at a speed of 1,100 m/s, flying 5 x 107 meters from the center of the planet. At a later point, the spacecraft reaches a new altitude, flying 8.6 x 107 meters from the center.