A student swings a ball at the end of a string of length R in a vertical circle as shown. The ball moves with the minimum speed necessary to complete a circular path at point 1. Consider the system of the ball. In terms of the mechanical energy of the system, which of the following claims is correct, and why?
A
The system is open, because the ball is able to complete a full revolution around the circle.
B
The system is open, because a net force is esbosted on the ball as it travels in a circle.
С
The system is closed, because the ball is able to complete a full revolution around the circle.
D
The system is closed, because the speed of the ball remains constant as it travels in the vertical circle