Concept #1: Satellite Speed

Practice: Suppose that you used some geometry and kinematics to estimate that the Earth goes around the Sun with an orbital speed of approximately 30,000 m/s (60,000 mph), and that the Sun is approximately 150 million kilometers away from the Earth. Use this information to estimate the mass of the Sun.

Example #1: Find speed of second satellite, given speed of first

Practice: You throw a baseball horizontally while on the surface of a small, spherical asteroid of mass 7×10^{16} kg and diameter of 22km. What is the minimum speed so that it just barely goes around the asteroid without hitting anything?

Concept #2: Satellite Period

Practice: A satellite orbits at an orbital period of 2 hours around the Moon. What is the satellite’s orbital altitude?

Example #2: Find mass of planet, given moon speed and period

Practice: A distant planet orbits a star 3 times the mass of our Sun. This planet of mass 8×10<sup>26</sup>kg feels a gravitational force of 2x10<sup>26</sup>N. What is this planet’s orbital speed and how long does it take to orbit once?