Answer:
C) 9.4 m/s
Explanation:
[tex]m_1[/tex] = Mass of moving car = 1200 kg
[tex]u_1[/tex] = Initial velocity of moving car = 21.1 m/s
[tex]m_2[/tex] = Mass of stationary car = 1500 kg
[tex]u_2[/tex] = Initial velocity of stationary car = 0
v = Velocity of the combined cars
As the momentum in the system is conserved we have
[tex]m_1u_1+m_2u_2=(m_1+m_2)v\\\Rightarrow v=\dfrac{m_1u_1+m_2u_2}{m_1+m_2}\\\Rightarrow v=\dfrac{1200\times 21.1+1500\times0}{1200+1500}\\\Rightarrow v=9.378\approx 9.4\ \text{m/s}[/tex]
The velocity of the combined mass is 9.4 m/s.