A sphere of mass \(0.5\text{ kg}\) is dropped into a column of oil. At the instant the sphere becomes completely submerged in the oil, the sphere is moving downward at \(8\text{ m/s}\), the buoyancy force on the sphere is \(4.0\text{ N}\), and the fluid frictional force is \(4.0\text{ N}\). Which of the following describes the motion of the sphere at this instant?