Mg photography Linyi

A, B, at the lowest point, the combined force of gravity and tension provides centripetal force. According to Newton's second law, F-mg=mv2r, so F > mg, so a is wrong and b is right;

C. The tension of the rope when the player swings to the lowest point and the tension of the player on the rope are the relationship between force and reaction. According to Newton's third law, they are equal in size and opposite in direction, and act on the same straight line, so C is wrong;

D, in the process of the player's movement to the lowest point, the mechanical energy is conserved, which is a circular movement with variable speed, and the pulling force is variable force, so D is wrong;

So choose B.