一、问题的提出江苏省淮阴中学2010届高三一次学情调研卷上有这样一道题目:如图1所示,Oa、Ob、Oc是竖直平面内三根固定的光滑细杆,O、a、b、c、d位于同一圆周上,d点为圆周的最高点,c点为最低点.每根杆上都套着一个小滑环(图中未画出),三个滑环都从O点无初速释放,用t_1、t_2、t_3依次表示滑环到达a、b、c所用的时间,则 First, the problem raised Huaiyin Middle School in 2010 in Jiangsu Province, the third year of high school history of a volume of research there is such a volume: As shown in Figure 1, Oa, Ob, Oc is a vertical plane three fixed smooth rod, O, b, c, d are located on the same circumference, d is the highest point of the circumference, c is the lowest point, and each rod is fitted with a small slip ring (not shown) No initial velocity release, with t_1, t_2, t_3 followed by the slip ring to reach a, b, c used by the time, then