Today, AP Physics 2 students complete the second activity in preparation of our visit to Fermilab: calculating the Mass of the Top Quark. I do this activity every year regardless of whether we are doing the Particle Physics Masterclass. I think it is a refreshing context in which to practice the application of the conservation of momentum in 2D. In addition, students find it fascinating how by setting c to 1, mass, energy, and momentum are numerically equivalent. Students also confront the uncertainty of how determine the angle of the momentum vector for an entire jet of particles. Between the two classes, the average mass of the top quark was calculated to be 181 GeV; a bit high.