Acceleration and Momentum (Physics Question)

Hello GMC! Today I have a question about acceleration and momentum using GameMaker's physics. I'm making a car racing game, and I'd like there to be bigger and heavier vehicles that accelerate slower but can hold up some steady momentum and don't get thrown off their path as easily as the little cars do. I was thinking density would affect this? Basically I'm wondering how one would go about doing something like that. I already have the cars moving and whatnot