Answer:
.
The common velocity of the two bodies after the collision is 2.7 m/s.
This can be calculated using the equation of conservation of momentum:
m1v1 + m2v2 = (m1 + m2)v
where m1 is the mass of the first body (12 kg), v1 is the velocity of the first body (4.2 m/s), m2 is the mass of the second body (18 kg), v2 is the velocity of the second body (0 m/s), and v is the common velocity of the two bodies after the collision.
Substituting the given values into the equation, we get:
12(4.2) + 18(0) = (12 + 18)v
Solving for v, we get:
v = 2.7 m/s