A Railroad Car Collides with and Sticks to an Identical

Multiple Choice

A railroad car collides with and sticks to an identical railroad car that is initially at rest. After the collision, the kinetic energy of the system

A) is one quarter as much as before.
B) is the same as before.
C) is one third as much as before.
D) is one fourth as much as before.
E) is half as much as before.