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% \begin{figure}[tb] \vspace{5pc}
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% \caption{Ladder for assignment~14.} \label{fig_lader} \end{figure}

\centerline{\bf Solution 22.5 set~6.} \bigskip

Using $\mu$ we can write 
$$ \vec{r}_1 = \frac{\mu}{m_1}\,\vec{r}\,,\qquad
   \vec{r}_2 = - \frac{\mu}{m_2}\,\vec{r}\,.          $$
Therefore,
$$ m_1\,\vec{r}_1\times\vec{v}_1 + m_2\,\vec{r}_2\times\vec{v}_2 =
   m_1\,\frac{\mu}{m_1}\,\vec{r}\times\vec{v}_1 - 
   m_2\,\frac{\mu}{m_2}\,\vec{r}\times\vec{v}_2 =  
   \mu\,\vec{r}\times\left(\vec{v}_1-\vec{v}_2\right) =
   \mu\,\vec{r}\times\vec{v}\ . $$
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