Ken and Kim are skating together on a rink at 3.00 m/s. Ken keeps asking Kim how much she weighs. Annoyed, Kim pushes away from Ken so that she speeds up to 4.00 m/s and he slows down to 2.40 m/s in the same direction. Friction, in the physics sense, is negligible in this drama. If Ken weighs 800 N, what does Kim weigh?