- #1

- 101

- 25

- Homework Statement
- A particle with unit mass has distance ##R## from the origin and initial speed ##u##. It moves in the central potential ##\Phi(r) = -k/r##. If it doesn't move in the central field, it would move in a straight line whose shortest distance from the origin is ##b## (impact parameter). When it moves in the central field, it's closest distance from origin is ##p < b## with speed ##w##. Assume ##u^2 \gg 2k/R##, find ##w^2/k## in terms of ##b, p## only.

- Relevant Equations
- ##l = bu##

The total energy of the particle is ##u^2 / 2 - k/R##. When ##u^2 \gg 2k/R##, we take the total energy to be ##u^2/2## only. By the conservation of energy, we have:

$$

\frac{u^2}{2} = \frac{w^2}{2} - \frac{k}{p}

$$

Take the angular momentum expression ##l = bu##, we can replace ##u## with ##b,l## thus getting an expression for ##w^2 / k## with ##b,p,l## only. But I don't know how to get an expression with ##b, p## only.

$$

\frac{u^2}{2} = \frac{w^2}{2} - \frac{k}{p}

$$

Take the angular momentum expression ##l = bu##, we can replace ##u## with ##b,l## thus getting an expression for ##w^2 / k## with ##b,p,l## only. But I don't know how to get an expression with ##b, p## only.

Last edited: