Realizing that you don't have as much experience with passenger trains, but just out of curiosity about the physics -- On a theoretical passenger train where t

Realizing that you don't have as much experience with passenger trains, but just out of curiosity about the physics -- On a theoretical passenger train where there is exactly zero coupler slack... say this train travels on a perfectly straight and level track so there's no need for coupler slack at all, maybe the cars are actually welded together for this experiment -- Would it be particularly difficult for a single engine to start the train? (Assume the train isn't ridiculously heavy or anything. This is really just curiosity about whether slack and/or draft gear make a difference when starting from a standstill.)