题目

If you go to a fast food restaurant or a snack bar, you will probably see a lot of teenagers．Today, many teenagers are overweight(超重的）, and some of this is because of their bad eating habits．Most teenagers love food with a lot of fat, oil, salt, and sugar．People often call this type of food “junk food”． But bad eating habits go beyond fast food．Many teenagers find it difficult to eat healthily．Some don’t have breakfast before they go to school．During the day, some don’t have a proper meal for lunch．In a recent survey at one school, scientists found that over tw如图所示．让钢球从斜面上由静止滚下，打到一个小木块上，能将木块撞出一段距离．放在同一水平面上相同位置的木块，被撞得越远，表示钢球的动能越大．现用质量不同的钢球从同一高度滚下，看哪次木块被推得远．回答以下问题：（1）设计实验的目的是研究______．（2）让不同的钢球从同一高度滚下是为了______．（3）此实验得出的结论是______．（4）下表中给出了一头牛慢步行走和一名普通中学生百米赛跑时的一些数据．物体质量（m/kg）速度v/m?s-1动能E/J牛约600约0.5约75中学生约50约6约900分析数据，可以看出，对物体动能大小影响较大的因素是______，你这样判断的依据是______．