This experiment uses a ballistic pendulum to determine the launch velocity of a metal ball. This is compared to a measurement of the launch velocity found using projectile motion. You may wish to emphasize why energy is not conserved in the initial impact of the ball into the ballistic pendulum, but momentum is, and conversely why energy is conserved as the pendulum rises but momentum is not conserved.
Data collection is pretty straightforward. A common problem people may have is that the "cannon" can be cocked to three different settings. It is important to make sure the students use consistent settings. Failure to do so will result in substantially different launch velocities.