1. Gravity is what causes physical bodies to move along a parabola. See this thread on implementing gravity: http://blitzbasic.com/Community/posts.php?topic=55946&hl=gravity
2. Set the object's velocity vector to 0 when you detect the collision. You'll need to loop through all your entities, checking each for collisions.
2. Set the object's velocity vector to 0 when you detect the collision. You'll need to loop through all your entities, checking each for collisions.