解答上述试题---**Question Stem:** [例1] 在图1-5-1中画出力 F_1、F_2 对支点 O 的力臂，并分别用字母 l_1、l_2 表示。 **Other Relevant Text:** 图1-5-1 **Chart/Diagram Description:** * **Type:** Physics diagram illustrating a lever system with forces and a pivot point. * **Main Elements:** * **Wall/Fixed Support:** A vertical line on the left side, indicated as fixed by a series of diagonal hashes. * **Pivot Point (O):** A small circle labeled 'O' located on the wall, where the rod is hinged. * **Rod/Lever:** A rigid body represented by a double line, attached to the pivot point O. It extends downwards and to the right. * **Force F_1:** An arrow labeled 'F_1' applied near the free end of the rod. The arrow points upwards and to the left, making an acute angle with the rod. * **Force F_2:** An arrow labeled 'F_2' applied at an intermediate point on the rod, between O and the point of application of F_1. The arrow points vertically downwards. * **Relative Position:** The rod is pivoted at its top-left end (O) on the vertical wall, extending downwards and to the right. Force F_2 acts downwards on the rod, and Force F_1 acts upwards and leftwards on the rod's rightmost end.