Final answer:
The student's assertion about increasing momentum during gravitational attraction is correct, but the reason provided is incorrect. The correct reasoning involves internal gravitational force and Newton's second law of motion, specifically conservation of momentum without external forces.
Step-by-step explanation:
The student's question involves understanding the momentum and forces in different physics scenarios. The assertion that two particles moving towards each other due to gravitational attraction will have increasing momentum is correct, assuming no other forces are acting on them. However, the reason given involving the rate of change of momentum depending on Fext'/A is incorrect; the correct explanation involves Newton's second law and gravitational force as the internal force between the particles, not an external force.
In the examples provided, when particles collide or when they strike a container wall, Newton's third law and the impulse-momentum theorem are important. The momentum is conserved in a system without external forces.
When considering changes in energy and forces between particles, it is necessary to consider the context. In general relativity, as energy increases, the effective mass of interacting particles could increase, affecting the gravitational force between them.