- #1

AbigailG

- 12

- 1

## Homework Statement

Two Jupiter sized planets are released from rest 1.0 X 10^11 m apart. What are their speeds as they crash together?

I think my problem lies in figuring out which radius to use. In an equation like this are the radii of the planets included in the distance between them given? If not, should it be?

## Homework Equations

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Ug = -Gm1m2/r

r (Jupiter) = 6.99 x 10^7 m

m (Jupiter) = 1.9 x 10^27 kg

r (between) = 1.0 X 10^11 m

## The Attempt at a Solution

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Using conservation of energy:

Ei = Ef

Question #1 -- Ei is entirely Ugi...is it 2(Ug) ?

Ef = K + Ugf

Question #2 -- Is there still gravitational potential here? And if so is the radius used equal to twice the radius of Jupiter?

Question #3 -- Is the kinetic energy found for both of the planets or just one?

I need clarification on quite a few points, I apologize...but i feel like once I understand this fully I will be able to work it out myself.