4.5

v = \frac{m_{1} v_{1}}{m_{1} + m_{2}}

${v = \frac{{{m_1}{v_1}}}{{{m_1} + {m_2}}}}$

v = \frac{m_{1} v_{1}}{m_{1} + m_{2}}

$v = \frac{{{m_1}{v_1}}}{{{m_1} + {m_2}}}$

v

$v$

m_{1}

$m_1$

m_{1}

$m_1$

1

v_{1}

$v_1$

1

m_{2}

$m_2$

1