Answer:
1094.6 km/h
Explanation:
[tex]v_2[/tex] = Speed of command module
[tex]v_1[/tex] = Speed of motor
m = Mass of motor
4m = Mass of module
v = Velocity of space vehicle = 5125 km/h
Relative velocity
[tex]v_2-v_1=87\ km/h\\\Rightarrow v_1=v_2-87[/tex]
As the linear momentum of the system is conserved
[tex](m+4m)v=4mv_1+mv_2\\\Rightarrow 5mv=4mv_1+mv_2\\\Rightarrow 5v=4v_1+v_2\\\Rightarrow 5\times 5125=4(v_2-87)+v_2\\\Rightarrow 5125=5v_2-348\\\Rightarrow v_2=1094.6\ km/h[/tex]
The speed of the command module relative to Earth just after the separation is 1094.6 km/h