Create a Train Physics system for a Train Simulator, realism is important!

Hi, We are building a Train Simulator, but need help on the physics. We need someone that has good experience with physics and maths. We wan't the system to be accurate and realistic, take OpenRails and TS2018 as a example. We are looking for someone wo can do that for us in a week, or even beter, has the formulas to get it to work(and how to combine them ofc.) You don't need to program and such, just provide us with some basic theory and formulas and how to combine them to get it to work. We are on a small budget as it is a free game. Contact will go via messaging or emailing.