问题
计算题
为了测量某住宅大楼每层的平均高度（层高）及电梯运行情况，甲、乙两位同学在一楼电梯内用电子体重计及秒表进行了以下实验，一质量为m＝50kg的甲同学站在体重计上，乙同学记录电梯从地面一楼到顶层全过程中，体重计示数随时间变化的情况，并作出了如图所示的图像，已知t＝0时，电梯静止不动，从电梯内楼层按钮上获知该大楼共19层。求：
（1）电梯启动和制动时的加速度大小；
（2）电梯上升的总高度及该大楼的层高。
答案
解：（1）对于启动状态应用牛顿第二定律得：
由图得出F1＝600N，代入数据解得：a1＝2m/s2
对于制动状态应用牛顿第二定律得：
由图得出F3＝400N，代入数据解得：a3＝2m/s2
（2）电梯匀速运动的速度为：
m/s
从图中读得，电梯匀速上升的时间t2＝26s，电梯运动的总时间t＝28s
所以总位移为：
＝54m
则有层高为：
m＝3m
affec
ted only the area immediately around large c
ities with factories and/or heavy automobile traffic. Today, we know that although these are the areas with the worst air pollution, the problem is literally worldwide. On several occasions over the past decade, a heavy cloud of air pollution has covered the entire eastern half of the United States and led to health warnings even in rural areas away from any major concentration of manufacturing and automobile traffic. In fact, the very climate of the entire earth may be affected by air pollution. Some scientists feel that the increasing concentration of carbon dioxide in the air resulting from the burning of fossil fuels(coal and oil) creating a greenhouse effect-holding in heat reflected from the earth and raising the world’s average temperature. If this view is correct and the world’s temperature is raised only a few degrees, much of the polar ice cap will melt and cities such as New York, Boston, Miami, and New Orleans will be under water.
United States
most brought worldwide effect