8. Centripetal Forces & Gravitation

Io and Ganymede are two of Jupiter's four Galilean moons. Io orbits at an average distance of 422,000km in 1.77 days. What is Ganymede's average orbital distance (in km), if it takes 4 times longer to orbit Jupiter?

According to Kepler's Third Law, which of the following planets (on average) takes the longest to orbit the Sun (has the longest orbital period)? $T^2=\frac{a^3}{k}$

Why is Newton's version of Kepler's Third Law so useful to astronomers?

According to Kepler's Third Law, what is the orbital period in Earth-years of a planet whose average distance from the Sun is $3$ astronomical units ($\mathrm{a.u.}$)?