Having worked with C2 physics quite a bit I can tell you it is not going to provide real world physics but is designed for games to give the illusion of physics.
Many factors in the real world simply can't be factored in to computed physics that happens in real time because a computer does not react in real time and is a string of events played in order one after the other. It does it super fast but will never match what happens in real life physics.
That being said, you can get some good simulations for studying the effects and teaching basic physics in C2 and you can look at Chipmunk physics by R0J0hound that allows more settings for parameters.
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I believe the 10 mark used on C2 is set to actual gravity but the units used are designed to be easier to implement.
There is a catapult example included in C2 and many good discussions on physics in the forum and tutorials to search that should help.