Final answer:
Additional upward force is required for equilibrium in situations C and D, where downward forces from a rope or a person exceed the gravitational force. In situation B, a force countering the component of gravity along the plane is needed, but it's not strictly 'upward.' Situation A and E already imply equilibrium without mentioning additional forces.
Step-by-step explanation:
To determine which situations require additional force in the upward direction for equilibrium, we need to analyze the scenarios in terms of forces and equilibrium states.
- Situation A: The box is on a flat surface with gravity acting downwards. Since it is not moving, the normal force from the surface balances the gravitational force, and no additional upward force is needed.
- Situation B: On an inclined plane, there is a component of gravitational force acting down the plane and a normal force perpendicular to the surface. To bring the box to equilibrium, an additional force would be needed to counteract the component of gravity parallel to the plane's surface. However, this force is not directly 'upward' in the sense of opposing gravity.
- Situation C: If a box is being pulled downward by a rope, assuming that this force exceeds the weight of the box, an additional upward force would be necessary to achieve equilibrium.
- Situation D: Similarly to situation C, if a person is pushing downward on the box with a force greater than the weight of the box, an additional upward force is needed for equilibrium.
- Situation E: When a box is being lifted by a crane, if the crane exerts an upward force equal to the weight of the box, no additional force is needed; but if it is greater, a downward force would be required to achieve equilibrium.
Forces such as tension, normal force, and friction can play a role in these situations to achieve or maintain equilibrium.