Ender and Shen are flying at each other during a battle in space. Ender moves with a velocity v1 of 12 m/s and Shen, with a mass of 45 kg, moves at a velocity v2 of 9.0 m/s. When the two collide, they hold on to each other and move with a velocity v3 of 6.4 m/s. What is Ender’s mass, in kg?

Emmy kicks a soccer ball up at an angle of 45° over a level field. she watches the ball's trajectory and notices that it lands, two seconds after being kicked, about 20 m away to the north. assume that air resistance is negligible, and plot the horizontal and vertical components of the ball's velocity as a function of time. consider only the time that the ball is in the air, after being kicked but before landing. take "north" and "up" as the positive ‑ and ‑directions, respectively, and use ≈10 m/s2 for the downward acceleration due to gravity.