For students building Sierra College Tech-Explorer catapults, you may find the following web sites useful in calculating the distance the ball will travel. Watch the movie showing how applied math has been integrated into the Tech-Explorer catapult project supported by Sierra College CACT, Sierra STEM Collaborative and the Sierra College National Science Foundation grant project.
http://www.phy.hk/wiki/englishhtm/ThrowABall.htm
http://publicliterature.org/tools/projectile_motion/
http://www.tinafad.com/projectile/index.php
http://www.netzmedien.de/projectilemotion/scripting.html