# what is the translational motion with the velocity of the center of mass?

and that is the internal motion relative to the center of mass? could give me some examples? desire to relate since I need to find out what is the kinetic energy in the center-of-mass of two particles, one moving and one stationary. Note: they collide

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$$x_\textrm{com} = \frac{m_1 x_1 + m_2 x_2}{m_1 + m_2}.$$
$$x'_1 = x_1 - x_\textrm{com},\ x'_2 = x_2 - x_\textrm{com}.$$