Computer-interfaced motion detectors are required to carry out this inquiry. It is a new twist on exploring motion with plunger carts: they are set back-to-back and then propelled away from each other. Their velocities are measured, and the procedure repeated with increasing masses. The experiment is meant for high school physics classes, as there is no step-by-step procedure to guide them. They will need to design their own procedures and prepare a lab report.  Embedded in the resource are links to associated reading and another related lab exercise.