Which of Kepler's laws directly relates to the observation that planets appear to move slower when they are farther from the Sun than when they are nearer?

On Earth, g ≈ 9.8 m/s2. If an object is moved to a location where g = 0, its mass:

The force with which the Earth attracts an object is called:

Two stars of masses m and 2m at a distance d rotate about their common centre of mass in free space. Their period of revolution is: