Answer:8.8 m/s
Explanation:
Given
mass of train [tex]m_1=0.6 kg[/tex]
velocity of Train [tex]v_1=20 m/s[/tex]
mass of another train [tex]m_2=1.5 kg[/tex]
Final velocity of both train [tex]v=12 m/s[/tex]
Let [tex]v_2[/tex] be the velocity of [tex]m_2[/tex] before collision
As external Force is zero therefore change in momentum is zero
conserving Momentum
[tex]m_1v_1+m_2v_2=(m_1+m_2)v[/tex]
[tex]0.6\times 20+1.5\times v_2=(0.6+1.5)\cdot 12[/tex]
[tex]1.5\times v_2=25.2-12[/tex]
[tex]v=\frac{13.2}{1.5}=8.8 m/s[/tex]