Particle physicists verify Einstein's famous equation E=mc2 every day in accelerators around the world. They convert energy into mass almost as commonly as you flip through channels on the television.
In 1995 physicists who work at Fermilab created the last and most massive quark ever discovered, the top quark, by converting mass into energy and then energy into mass!
You can use the principle of conservation of momentum which you have been studying and 1995 experimental data to determine the mass of the top quark. The D-Zero Experiment