As shown in the picture, when the "Time Travel" is extremely fast, the actor is driving a motorcycle and hovering up and down on the inner wall of the spherical metal mesh, which is very amazing. During the circular motion of the motorcycle along the vertical track shown in the figure,

A. mechanical energy must be conserved.

B. its output power is always constant.

C the centripetal force through the lowest point is only provided by the supporting force.

The minimum speed when d passes through the highest point is related to the diameter of the spherical metal mesh.

Analysis: d, in the process of circular motion of motorcycle on vertical track, both friction force and engine power have to do work, and mechanical energy is not conserved; In the process of motorcycle movement, its force and movement are constantly changing, and its output power is also constantly changing. At the lowest point, the centripetal force is provided by the combined force of gravity and support. When passing through the highest point, the centripetal force at the minimum speed is only provided by gravity.