4e.6 A 10-kg box is pulled across the frictionless floor by a 50.0-N pulling force F1, directed at 36.90 above the horizontal. Another pulling force F2 is applied to the left, making the box moving with a constant velocity. Calculate: (a) the horizontal pulling force F2, and (b) the normal force on the box. [Answer: (a) 40 N, (b) 70 N]