原题(第28届全国中学生物理竞赛复赛试题二)质量均匀分布的刚性杆AB、CD如图1放置,A点与水平地面接触,与地面间的静摩擦系数为μ_A,B、D两点与光滑竖直墙面接触,杆AB和CD接触处的静摩擦系数为μ_C,两杆的质量均为m,长度均为l。(1)己知系统平衡时AB杆与墙面夹角为θ,求CD杆与墙面的夹角α应该满足的条件(用α及已 The original title (the 28th National Secondary School Physics Competition Rematch question two) the mass evenly distributed rigid rods AB, CD placed in Figure 1, A point with the horizontal ground contact with the ground static friction coefficient μ_A, B, D and Smooth vertical wall contact, rod AB and CD at the contact static friction coefficient μ_C, the quality of the two rods are m, the length is l. (1) In the known system, the angle between AB rod and wall is θ, and the condition that the included angle α between CD rod and wall should satisfy (α and