题目内容
用一个机械将货箱全部吊上离地12 m高的平台,现有30个货箱,总质量为150 kg,这个机械在吊箱子时所能提供的功率取决于所吊物体质量的多少,如下图所示(不计放下吊钩、搬起和放下箱子等时间,每次起吊过程箱子均做匀速运动,g=10m/s2).根据图线可得出下列结论,其中错误的是( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250017538886069.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250017538886069.jpg)
A.每次吊起3个货箱,吊完货箱所需时间最短 |
B.吊完所有货箱至少需要12min |
C.每次吊起的货箱越多,上升速度越小 |
D.一次吊起3个货箱时,上升速度最大 |
D
试题分析:根据图线知,当吊起的质量为15kg时,功率为25W,则吊起的速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001753903877.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001753935625.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001753950627.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001753966673.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825001753981695.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250017539971129.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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