일반물리학 1 — Kinetic Energy and Work: Problem 15

15. Figure 7-21 shows three forces applied to a trunk that moves leftward by 3.00 m over a frictionless floor. The force magnitudes are \(F_1 = 5.00 \text{ N}\), \(F_2 = 9.00 \text{ N}\), and \(F_3 = 3.00 \text{ N}\), and the indicated angle is \(\theta = 60.0^\circ\). During the displacement, (a) what is the net work done on the trunk by the three forces and (b) does the kinetic energy of the trunk increase or decrease?