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Oomph!

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1. Homework Statement

1. Homework Statement

I have to find formula for effective cross-section (

*σ*) of catching a comet with the Sun. I know mass of the Sun (

*M*), radious of the Sun (

*R*) and initial velocity (

*v*) of the comet (at a big distance from the Sun).

## Homework Equations

σ=πb^2, where b is on the picture (

*b*>

*R*)It is the biggest distance when the Sun still catch the comet.

## The Attempt at a Solution

I really don't know how to work with the

*b.*It is semi-minor axis in in an elliptical trajectory of the comet. However, I don't know semi-major axis or linear eccentricity...

I just know the initial velocity

*v*of the comet. I think I sould work with energy or angular momentum at the beginning and near the catching. However, I still have there some distances which I don't know.

Please, could you give me an advice?

Thank you.