here at the moment when bullet strikes the block it will have no external force on it
so here we can use momentum conservation
so we will have
[tex]P_i = P_f[/tex]
[tex]m_1v_{1i} + m_2v_{2i} = m_1v_{1f} + m_2v_{2f}[/tex]
[tex]0.03(200) + 3(0) = 0.03v + 3v[/tex]
[tex]6 = 3.03v[/tex]
[tex]v = \frac{6}{3.03}[/tex]
[tex]v = 1.98 m/s[/tex]
so they move together with speed 1.98 m/s