---
title: "A planet has two moons, Moon A and Moon B, which both travel in circular orbits. The orbital radius of Moon B is nine times the orbital radius of Moon A (\\(r_B = 9r_A\\)). Both moons are held in their orbits solely by the gravitational pull of the planet. What is the ratio of the orbital period of Moon B to the orbital period of Moon A, \\(T_B / T_A\\)?"
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url: "https://nerd-notes.com/ubq/109502/"
date_modified: "2026-03-25T04:13:05+00:00"
---

# A planet has two moons, Moon A and Moon B, which both travel in circular orbits. The orbital radius of Moon B is nine times the orbital radius of Moon A (\(r_B = 9r_A\)). Both moons are held in their orbits solely by the gravitational pull of the planet. What is the ratio of the orbital period of Moon B to the orbital period of Moon A, \(T_B / T_A\)?

A planet has two moons, Moon A and Moon B, which both travel in circular orbits. The orbital radius of Moon B is nine times the orbital radius of Moon A (\(r_B = 9r_A\)). Both moons are held in their orbits solely by the gravitational pull of the planet. What is the ratio of the orbital period of Moon B to the orbital period of Moon A, \(T_B / T_A\)?

![A central planet is shown with two concentric circular paths around it. The inner path is labeled Moon A with a dashed line indicating a radius r_A. The outer path is labeled Moon B with a dashed line indicating a radius r_B. Moon B's orbit is shown significantly further from the planet than Moon A's orbit.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1774411984-gBy2MR.jpg)

- **A.** 3
- **B.** 9
- **C.** 27
- **D.** 81

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/109502/*