TBR Physics Question

[moose45]

When Johannes Kepler, 17th-century astronomer and smart guy, predicted a relationship between the mean orbital radius and orbital period of a planet about the sun, he found that the period squared is:

A. proportional to the cube of the orbital radius.
B. proportional to the square of the orbital radius.
C. proportional to the orbital radius
D. proportional to the square root of the orbital radius.

Anyone know how to solve this problem? Thanks!

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[loveoforganic]

Pretty sure it's A, but I'm also pretty sure that's just something you'd have to have memorized. Unless that could maybe be figured out with the knowledge that planets' orbits are ellipses.

 

[EyEnStein 07]

I think its his 3rd law

P^2 (proportional) a^3

so yes, its A

 

[moose45]

yeah its A, its a formula we have to memorize.