A hockey puck moving horizontally with a velocity of 20 m/s strikes two other pucks which are stationary. After the collision, the first puck has a velocity of 5.0 m/s in the same direction as its original motion, and one of the other pucks moves with a velocity of 10 m/s at an angle of 60° below the horizontal. Determine the velocity of the third puck if all of the pucks have the same mass. *Note: Show all your work/calculations.