题目

Here is a part from Maria’s diaries(日记) about her vacation. The 3rd Day: Yesterday we arrived in London in the rain. We went to some big shops. The 4th Day: We came to Paris. The day was cloudy and the food wasn’t good. We liked the shops here, but the things were dear. The 5th Day: We arrived in Rome in the hot weather. We had lunch in a small restaurant, and the food was delicious. We visited some shops. They were all wonderful. The 6th Day: We went to New York and the things in the shops were all dear. But we liked the warm weather there. The 7th Day: Today we visited Ne在“研究平抛物体运动”的实验中，可以描绘平抛物体运动轨迹和求物体的平抛初速度。（1）实验简要步骤如下：A．让小球多次从斜槽上同一位置上由静止滚下，记下小球落在接球凹槽的一系列位置B．安装好器材，注意斜槽末端水平和平板竖直，记下斜槽末端O点和过O点的竖直线C．测出曲线上某点的坐标x、y，算出该小球的平抛初速度，实验需要对多个点求v0的值，然后求它们的平均值D．取下白纸，以O为原点，以竖直线为轴建立坐标系，用平滑曲线画平抛轨迹上述实验步骤的合理顺序是_（只排列序号即可）；步骤C中计算小球平抛运动的初速度的表达式为________。（2）在探究平抛运动规律的实验中，下列关于实验误差的的说法，正确的是_______。A．若斜槽轨道末端没有调整水平，会导致误差B．斜槽轨道的不光滑会产生误差C．为减小实验误差，实验小球应选用质量较大、体积较小的金属球D．小球在斜槽轨道上释放点的高度越高，实验误差越小（3）某同学在做平抛运动实验时得到了如图所示的物体运动轨迹，因没有记录轨道末端位置，在轨迹上任取一点a为坐标原点建立如图的坐标系（y轴竖直，x轴水平），又在轨迹上另取b、c两点的位置（如图），（g取10m/s2）则小球平抛的初速度为________m/s。