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# Two bodies of masses 10 kg and 2 kg are moving with velocities $2m/s$ and $10m/s$, towards each other . The velocity of their centre of mass is

$\begin {array} {1 1} (a)\;\frac{10}{3}\;m/s & \quad (b)\;5\;m/s \\ (c)\;2\;m/s & \quad (d)\;zero \end {array}$

$\bar {v} _{cm}=\large\frac{ m_1 \bar {v}_1+m_2 \bar {v}_2}{m_1+m_2}$
$\qquad=\large\frac{10 \times 2 -2 \times 10}{12}$
$\qquad=0$