A railroad car containing explosive material is initially traveling south at a speed of 5.0 m/s on level ground. The total mass of the car plus explosives is 3.0 × 10⁴ kg. An accidental spark ignites the explosive, and the car breaks into two pieces, which then roll away along the same track. If one piece has a mass of 2.0 × 10⁴ kg and a final speed of 2.5 m/s toward the south, what is the final speed of the other piece?