i am creating a game similar to this.

[matches81]

@Spooder Wekd:
Sorry for the misunderstanding, but to me your first post seemed more like "you don't know that so you shouldn't be making games".
I agree with everything you said in your second post, though, except that I still think using a third-party engine is the only way a lot of people will actually finish a game. Although I wouldn't say "never write your own engine when there's so many good free ones around" (I heard that quite a few times, though), I'd still advise people looking to make games to have a good look at their options.

@maxdelphi:
If you have a physics engine running in the background, the only thing you need to figure out is how much force you need to apply to an object to get the desired throw range. There shouldn't be a formula involved, the physics engine should take care of that for you.
The simplest way to get that "throwing force": Trial & error. Just pop in a few rough values until you get to a point that seems reasonable to you, then tweak it.