a,
$\vec{v_1}$ ngược chiều $\vec{v_2}$
$\Rightarrow m_1v_1 - m_2v_2= (m_1+m_2)v$
$\Leftrightarrow v= \frac{m_1v_1-m_2v_2}{m_1+m_2}= 0,6 (m/s)$
b,
$\vec{v_1}$ vuông góc $\vec{v_2}$
$\Rightarrow (m_1v_1)^2+ (m_2v_2)^2= [(m_1+m_2)v]^2$
$\Leftrightarrow v= \sqrt{\frac{(m_1v_1)^2+ (m_2v_2)^2}{(m_1+m_2)^2}}= 3 (m/s)$
$\Delta P_1= P - P_1= m_1v - m_1v_1= -3 (kg.m/s)$
$\Delta P_2= P-P_2= m_2v - m_2v_2= -3 (kg.m/s)$