I need some help on how to solve this question, I don't really know how to do this at all. A vessel at rest explodes, breaking into three pieces. Two pieces having equal mass, fly off perpendicular to one another with the same speed of 30 m/s. The third piece has three times the mass of each other piece. What are the magnitude and direction of it's velocity immediately after the explosion? I was told that the sum of the potential energy has to equal the final kinetic energy, but isn't there no potential energy at the beginning?