To calculate the force on the rock, the mass and change in velocity during the contact time are required. Without these details, the magnitude of the force cannot be determined.
To determine the magnitude of the constant force acting on the rock, additional information would be necessary, such as the mass of the rock and any changes in velocity. The given scenarios do not directly provide the details needed to solve for the force in the student's question. However, generally, one would use Newton's second law, F = ma, where m is mass and a is acceleration. To get acceleration, you would need the initial and final velocities during the contact time. Without such details, we cannot provide a final answer to the magnitude of the force.