If a minecart hits another minecart that is travelling in a perpendicular direction, what happens to the component velocities? Is the behaviour different if the carts collide while in midair? Call it the T-bone aiming system if it works.
Okay, tried it, with two perpendicular 10-tile impulse ramp accelerators that converge on a NSEW flat track. Both carts start with 0 offset on the exact same tick.
Prior to colliding, both carts have the same speed, 112,470, in their respective directions.
On the tick where collision occurs, one cart enters the point of convergence of the tracks. The other comes to a halt one tile before that point. The cart that enters the point of convergence does retain the full velocity of both carts, in addition to an extra 5000 from the other cart, so it has slightly more speed in the direction of the non-continuing cart. That cart is now traveling at a 45 degree angle.
That's the good news. The bad news is what happens to the contents of the carts. Both eject their contents on the tick where collision occurs. Both ejected contents appear to have their velocities based just on the speed of each cart before the collision, so both are still traveling orthogonally.
The tick after collision, the stopped cart moves into the tile at the point of convergence and stays there. The other cart moves away at 45 degrees and all the ejected contents fly along orthogonal trajectories, not showing any effect of the collision.
Summary, you can get a cart going in a non-orthogonal direction with a collision, but this test didn't reveal a way to fire non-cart projectiles at an angle.