Question

A student stands at one end of a raft floating in a pool with equally spaced marks along the bottom. The student and the raft have the same mass. The student walks to the opposite end of the raft. Which of the following best shows the final location of the raft and the student relative to the marks at the bottom of the pool? Assume that there is no drag force between the raft and the water?

1) The raft moves towards the student
2) The raft moves away from the student
3) The raft stays in the same position
4) The raft sinks

Answer 1

The raft moves away from the student when the student walks to the opposite end due to the conservation of momentum and Newton's third law of motion.

Step-by-step explanation:

A student stands at one end of a raft floating in a pool and walks to the opposite end. Among the given options, the one that best represents the final location of the raft and the student relative to the marks at the bottom of the pool is: The raft moves away from the student.

When the student moves towards the other end of the raft, due to Newton's third law of motion, the raft will exert an equal and opposite force on the water beneath it, causing the raft to move in the opposite direction of the student's walk. This is because the momentum of the system (student plus raft) is conserved since there is no external horizontal force acting on the system. Thus, as the raft experience a force in the opposite direction to the student's walk, it will move toward the original position of the student relative to the marks at the bottom of the pool.

Therefore, the correct answer is that the raft moves away from the student, which is option 2. This phenomenon can be observed in day-to-day examples such as the relative motion of a boat being pushed across a bathtub.