\(\because\) momentum is conserved

\(P _{ i } \overrightarrow{=0}\)

\(P _{ f }= m _{ f ( A )} V _{( A )}+ m _{ f ( B )} V _{( B )}=0\)

\(m _{ f ( A )} V _{( A )}^{\overrightarrow{ A }}=- m _{ f ( B )} V \underset{( B )}{\overrightarrow{ }}\)

both move in opposite directions

\(\because m _{ f ( B )} \equiv m _{ f ( A )}\)

\(V _{\vec{A}} \equiv V _{\vec{B}}\)