Final answer:
Robert does positive work on the box by applying a force in the direction of the box's motion, overcoming friction to maintain constant speed.
Step-by-step explanation:
Robert pushes the box to the left at constant speed, and in doing so, Robert does positive work on the box. According to physics, work is defined as the product of the force applied in the direction of motion and the distance over which it acts. In the scenario presented, if Robert is applying force to move the box in a horizontal direction and the box is moving, then the displacement of the box is parallel to the force applied by Robert, resulting in positive work. It is important to note that moving the box at constant speed indicates that the net force on the box is zero; however, Robert must apply a force to counteract friction and maintain constant speed. As he exerts a force to keep the box moving, he is continuously doing work.