先看2008年上海市的一道春季高考题:某厂根据市场需求开发折叠式小凳(如图1),凳面为三角形的尼龙布,凳脚为三根细钢管.考虑到钢管的受力和人的舒适度等因素,设计小凳应满足:凳子高度为30cm,三根钢管相交处的节点O与凳面三角形ABC重心的连线垂直于凳面和地面. Let’s look at a spring entrance examination in Shanghai in 2008. According to market demand, a factory develops a folding stool (Fig. 1). The stool surface is a triangular nylon cloth. The foot of the stool is three thin steel tubes. Considering the force of the steel tube and Human comfort and other factors, the design stool should meet: stool height of 30cm, the intersection of the three nodes at the intersection of steel pipe O and the center of gravity of the stool surface triangle ABC perpendicular to the bench surface and the ground.