Solution: (1) Let the linear velocity of the ball be V and the radius be R.

Then in a, f+mg = mv2r ①.

F' at c？ mg=mv2R②

△ f = f'-f = 2mg = 2n is given by ① ② formula.

(2) The force that the exerciser needs to apply when he is in position A is F,

Centripetal force f direction of a ball moving in a uniform circle =F+mg,

In the best case, there is no friction,

Force analysis is shown in the figure.

Then tan θ = f to mg = f+mgmg = f+ 1.

The diagram of tanθ-F is shown in the figure.

Answer: (1) The force that bodybuilders need to exert at point C is 2n greater than that at point A;

(2) The diagram of tan θ-f is as shown in the figure.