# How would you calculate the length of a year on a planet?

#### songminho

Poster has been reminded to fill out the full HH Template in future schoolwork threads
1. The problem statement, all variables and given/known data
How would you calculate the length of a year in Earth years on a hypothetical planet? (given the mass + radius of the planet)

I understand Kelper's law is used somehow, but is orbital velocity needed?

Related Introductory Physics Homework News on Phys.org

#### rude man

Homework Helper
Gold Member
Try Law #3, "The Law of the Periods".
The radius of the planet is a no-count. So is the mass.

#### J Hann

You can start with: gravitational attraction = centripetal force
G M m / R^2 = m v^2 / R
I assume that by radius is meant the radius (mean) of the planet's orbit.
Note that the period can then be calculated in terms of v and R.

### Want to reply to this thread?

"How would you calculate the length of a year on a planet?"

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving