An Empty Railroad Car Traveling at a Constant Speed Strikes

Multiple Choice

An empty railroad car traveling at a constant speed strikes a second car at rest.The second car,being full with passengers,has twice the mass of the first car.If the cars lock together as a result of the collision,the ratio of the initial to the final kinetic energies of the system is

A) 1.
B) 1/3.
C) 3.
D) 1/9.
E) 9.