Which of the following statements about work is or are true? (More than one statement may be true.)
A. Negative net work done on an object always reduces the object's kinetic energy.
B. If the work done on an object by a force is zero, then either the force or the displacement must have zero magnitude.
C. If a force acts downward, it does negative work.
D. The formula W = Fd cos theta can be used only if the force is constant over the distance.