Final answer:
The correct statement when two objects are in contact and moving together is that they must have the same acceleration, as dictated by Newton's second law. Additionally, per Newton's third law, they exert equal and opposite forces on each other regardless of their masses.
Step-by-step explanation:
When two objects are in contact and moving together, the correct statement that must be true is that the objects must have the same acceleration. According to Newton's second law, represented as F = ma, the net force acting on an object is directly proportional to its acceleration. This implies that if two objects are moving together without separating or changing their relative motion, they must be accelerating at the same rate. Additionally, per Newton's third law, whenever one object exerts a force on a second object, the second object exerts an equal and opposite force back on the first. Even if one object is more massive and therefore has a greater weight, they will exert equal but opposite forces on each other when in contact. Therefore, the objects do not need to have the same weight or the same net force acting on them, but they must exert the same magnitude of force on one another in accordance with Newton's third law.