A ball is fired from the projectile launcher across the room into a box. A microphone near th launcher starts a timing program in the computer, which clocks the flight until the impact of the ball on the back of the receiving box. Another microphone inside the box stops the computer
The distance between the cannon's muzzle and the impact point in the box divided by the time gives the horizontal velocity. The horizontal velocity can then be used to relate a given time to a horizontal discplacement. It can also be related to the vertical discplacement at the same point in time (remembering to take into account the initial height of the cannon) by the initial vertical velocity V(y)=V(x)/tan(theta).
Now a loop can be clamped to a two-meter stick at the correct vertical displacement, and a plamb line hung from it to correct the horizontal alignment. The cannon can be fired again (the student holding hteloop should be wearing safety glasses) and the ball should pass directly through the center of the loop on its flight.