Lời giải:

\[T = \frac{{2\pi }}{\omega } \Rightarrow \omega = \frac{{2\pi }}{T}\]\[ \Rightarrow {\omega _1} = \sqrt {\frac{k}{}} = \frac{{2\pi }}{{0,6}} \Leftrightarrow \frac{k}{} = \frac{{100{\pi ^2}}}{9} \Rightarrow {m_1} = \frac\](kg)

\[{\omega _2} = \sqrt {\frac{k}{}} = \frac{{2\pi }}{{0,8}} \Leftrightarrow \frac{k}{} = \frac{{25{\pi ^2}}}{4} \Rightarrow {m_2} = \frac{{25{\pi ^2}}} = \frac(kg)\]

\[ \Rightarrow \omega ' = \sqrt {\frac{k}{{{m_1} + {m_2}}}} = \sqrt {\frac{k}{{\frac{k}}}} = 2\sqrt {10} = 2\pi (rad/s)\]\[ \Rightarrow T' = \frac{{2\pi }}{{\omega '}} = \frac{{2\pi }}{{2\pi }} = 1(s)\]