21. in which one of the following circumstances does the principle of conservation of mechanical energy apply, even though a nonconservative force acts on the moving object? (a) the nonconservative force points in the same direction as the displacement of the object. (b) the nonconservative force is perpendicular to the displacement of the object. (c) the nonconservative force has a direction that is opposite to the displacement of the object. (d) the nonconservative force has a component that points in the same direction as the displacement of the object. (e) the nonconservative force has a component that points opposite to the displacement of the object.