１两种运动模型 ［例１］如图１所示，可视为质点的小球以初速度Ｖｎ沿水平轨道运动，然后进入竖直平面内半径为Ｒ的圆形轨道，若不计轨道的摩擦，为使小球能通过圆形轨道的最高点，则Ｖｏ至少应为多大？ ［例２］如图２所示，长度为ｌ的无动力“翻滚过山车”以初速度Ｖｏ沿水 1 Two kinds of motion model [Example 1] As shown in Fig. 1, a small ball that can be regarded as a mass point moves along a horizontal orbit with an initial velocity Vn, and then enters a circular orbit with a radius R in the vertical plane, excluding the orbital friction. In order for the ball to pass the highest point of the circular orbit, how large should Vo be? [Example 2] As shown in Fig. 2, a non-powered “rolling roller coaster” of length l with initial velocity Vo along the water