1. ?? Figure 1??, ???? angular momentum? P? ??? ????.
$\mathbf{r}_{P/O} = (-10\mathbf{i} + 20\mathbf{j} + 30\mathbf{k})$ cm, $m_A = 0.2$ kg, $m_B = 0.4$ kg, $m_C = 0.1$ kg, $\mathbf{r}_{A/O} = \mathbf{r}_{B/O} = \mathbf{r}_{C/O} = (50\mathbf{i} + 40\mathbf{k})$ cm, $\mathbf{v}_A = (10\mathbf{i} + 5\mathbf{j})$ cm/s, $\mathbf{v}_B = (2\mathbf{i} + 2\mathbf{k})$ cm/s, and $\mathbf{v}_C = (-5\mathbf{j} - 5\mathbf{k})$ cm/s.