Help with game logic

[Kenenth]

I am developing a game in which the user fires at oncoming troops. What would be the most efficient way to do these things: detect collision between a bullet and a troop, move a bullet based on a slope, and move across the screen? Any help is appreciated. I know that it is a very vague question, but I am just trying to see how I can go about this task while being as efficient as possible. Thanks!

[newDev]

Look into cocos2d, it is a game engine that has all the physics you'll need your game.

[davidlxk]

you should try Box2D with cocos2D. try this tutorial

How To Use Box2D For Just Collision Detection with Cocos2D iPhone | Ray Wenderlich

and also this

How To Create A Game Like Tiny Wings Part 1 | Ray Wenderlich