在竞赛试题中碰到变力做功,往往用功的公式难以求解其大小.通过分析物体做功与物体重心的位置有关,物体的重心升高,物体重力势能将增加,从而增加的重力势能需要克服物体重力做功成为解答这类竞赛题的突破口和切入点.现举例如下.例1.重为G,长为L均匀直棒悬于A点成竖直状态,现在 It is difficult to solve the problem by using the formula of force in the competition test. The analysis of the object’s work is related to the position of the object’s center of gravity. The center of gravity of the object is increased, and the potential energy of the object will increase, and thus the increased gravitational potential energy needs to overcome the object. Gravity work has become a breakthrough point and point of entry for answering such competition questions. The following examples are given below. Example 1. The weight is G, the length is L. The straight rod is suspended at point A and becomes vertical. Now