Answer:
Explanation:
Hello! To solve this problem we must be clear about the concept of energy conservation, and kinetic energy with the following sentence
The kinetic energy of the two cars (v = 1.2m / S) plus the kinetic energy of the third car (v = 3.5m / S) must be equal to the kinetic energy of the three cars together.
The kinetic energy is calculated by the following equation.

m= mass of the cars=26500kg
V=speed
E=kinetic energy
taking into account the above, the following equation is inferred
1= the cars are separated
2=
the cars are togheter
E1=E2

where
m= mass of each car
V1= 1.2m/s
Va=3.5,m/S

m= mass of each car
V=speed (in m/s) of the three coupled cars after the first couples with the other two
Solving



the speed of the three coupled cars after the first couples with the other two is 2.245m/s