three guns are aimed at the center of a circle, and each fires a bullet simultaneously. the directions in which they fire are 1200 apart. two of the bullets have the same mass of 4.5 x 10-3 kg and the same speed of 324 m/s the other bullet has an unknown mass and a speed of 575 m/s. the bullets collide at the center and mash into a stationary lump. what is the unknown mass of the third bullet?