## GR0177-22 Need More Detailed Explaination

Wanna Be Physicist
Posts: 27
Joined: Thu Dec 29, 2005 8:56 pm

### GR0177-22 Need More Detailed Explaination

Okay guys. I read Yosofun's solution but it seems like one has more variables than equations to solve for velocity, period, and mass of the planet.

I know (E) is automatically eliminated since semimajor axis is the same as maximum distance.

But Kepler's Third Law States

T^3 = (4 * pi^2/GM) * r^2

You you NEED M the mass of the planet to solve for T the period.

You also NEED M the mass of the planet to solve for v the minimum speed using the conversation of energy:

-k/(2a)=1/2mv^2-k/r

where k = GMm/r

It seems we have three unknown variables T, M, v and only two equations.

Am I missing something??

Wanna Be Physicist
Posts: 27
Joined: Thu Dec 29, 2005 8:56 pm

### Never Mind

I figured it out. Never Mind.

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