The problem is this: we can assume that the charge at the center of the circle is positive first, then from the running track, the charge running along PM must be positive, because like charges repel each other! Therefore, if the center of the circle is upward, the work must be repulsive, and the distance is greater than the former, so the speed of doing positive work will increase; The one along PN must be negative, which attracts the central charge. Center up, gravity is doing work, and the distance is greater than the former, so the speed is getting smaller and smaller when doing negative work; Do you understand this explanation?