What does "A" represent in a double replacement action?

When the force acting on an object points at least partially in the direction of the motion the work done is considered to be negative

Aperson stands on a platform, initially at rest, that can rotate freely without friction. the moment of inertia of the person plus the platform is ip. the person holds a spinning bicycle wheel with its axis horizontal. the wheel has moment of inertia iw and angular velocity ωw. take the ωw direction counterclockwise when viewed from above. part a what will be the angular velocity ωp of the platform if the person moves the axis of the wheel so that it points vertically upward?

Explain earth's motion, using the terms "precession" and "rotation" in your answer.