Answer:
2 m/s
Explanation:
[tex]m_1[/tex] = Mass of red truck = 1000 kg
[tex]m_2[/tex] = Mass of green truck= 3000 kg
[tex]u_1[/tex] = Initial Velocity of red truck = 6 m/s
[tex]u_2[/tex] = Initial Velocity of green truck
[tex]v[/tex] = Velocity with which they move together = 0
For elastic collision
[tex]m_1u_1 + m_2u_2 =(m_1 + m_2)v\\\Rightarrow m_1u_1 + m_2u_2 =0\\\Rightarrow m_1u_1 + m_2u_2 =(m_1 + m_2)v\\\Rightarrow m_1u_1 + m_2u_2 =0\\\Rightarrow u_2=-\frac{m_1u_1}{m_2}\\\Rightarrow u_2=-\frac{1000\times 6}{3000}\\\Rightarrow u_2=-2\ m/s[/tex]
Velocity of the green truck is 2 m/s