When gravity is the only force doing work on an object that moves from an initial height to a final height, the change in the object’s gravitational potential energy ΔUg is
a) ΔUg is always zero because gravity is a conservative force
b) ΔUg is equal in magnitude and identical in sign to the work done by gravity on the object
c) ΔUg is equal in magnitude and opposite in sign to the work done by gravity on the object
d) ΔUg is equal to the total work done by all forces acting on the object