A ballot box with mass m = 6.0 kilogram slides with speed v= 4.0 m/s across a frictionless floor in the positive direction of the x axis. The box explodes into two pieces. One piece, with mass m1 = 2.0 kilogram, moves in the positive direction of the x axis v1= 8.0 m/s. Find the velocity of the second piece, with mass m2?