解:Fn=m RArO ∑F=0,∑ Fr cOS-F=0 A ∑F=0,∑ Fr si 6 Fn=O B 令40.→、0. 2 mro FA=02兀 Ro2 cos0 de 2丌 0 ro sin 0 de=mRo? 2丌解: 2 2    R R R m F m a i n Ii = i i = Fx = 0, FIi cos − FA = 0 Fy = 0, FIi sin  − FB = 0 令 → 0,  i        2 mR R 2 m F 2 2 2 0 A = =  cos d        2 mR R 2 m F 2 2 2 0 B = =  sin d