We have two ballistics carts, but one works reliably and the other one is blue.
The ballistics cart demonstrates the independence of horizontal and vertical coordinates by showing that gravity only acts on the vertical component of velocity. Set it up on a track with a ball primed in the chute. Give the cart a push and, when the ball launcher photogate is tripped, the ball will fire upwards, adding a vertical component to its velocity. If you have prepared the appropriate burnt offerings and the physics gods deem you worthy, the ball will land back in the cart, demonstrating the constant horizontal component of velocity.