There are many factors as mentioned that come into play but just talking about the sheer force you take a 2 ton truck going 100 mph and a baseball, that ball would have to travel at 400,000 mph to have the same force on impact. Then you would need to look at how the force is applied to the body, the ball would have a limited area of impact and more than likely just penetrate the body doing less overall damage where as the truck would spread the force over a larger area.