A12,000kg. railroad car is traveling at +2m/s when it
strikes another 10,000kg. railroad car that is at rest. if the
cars lock together, what is the final velocity of the two
railroad cars?

The final velocity of the two  railroad cars is 1.09 m/s

Explanation:

Since we are given that the two cars lock together it shows that the collision is inelastic in nature. The final velocity due to inelastic collision is given by  

where

V= Final velocity

M1= mass of the first object in kgs = 12000

M2= mas of the second object in kgs = 10000

V1= initial velocity of the first object in m/s = 2m/s

V2= initial velocity of the second object in m/s = 0 (given at rest)

Substituting the given values in the formula we get

V = 2×12000 + 0x100012000 + 10000= 2400022000= 1.09 m/s  

Which is the final velocity of the two  railroad cars

it is the second option.

does anyone know or what?