PhySP18SS6.5.21 Let the cosine ONLY tell you whether the force does positive work or negative work over the displacement. If the angle bewtten the Froce vector and the Displacement vector is in the 1st or 4th quadrant that force will do positive work and will increase the kinetic energy of the system. It the angle between force and displacement is in the 2nd or 3rd quadrant then the force will do negative work on the system and the system will lose kinetic energy and therefore slow down.