题目内容
运用知识解决问题:如图所示,小明用动滑轮来提升重物,物体的重力为200N,手拉绳的力是150 N(不考虑绳重和摩擦),则滑轮的机械效率多大.
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_ST/images0.png)
【答案】分析:已知物重、拉力和承担物重的绳子段数,利用公式η=
×100%=
×100%=
×100%=
×100%可求出滑轮组的机械效率.
解答:已知:物体的重力为G=200N,手拉绳的力是F=150N,n=2
求:滑轮的机械效率η=?
解:滑轮的机械效率:
η=
×100%=
×100%=
×100%=
×100%=
×100%≈66.7%.
答:滑轮的机械效率为66.7%.
点评:此题考查了滑轮组的特点和机械效率计算公式及其变形的应用,需要熟练掌握基本规律,知道机械效率的变形公式η=
×100%=
×100%=
×100%=
×100%是解决此题的关键.
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/0.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/1.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/2.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/3.png)
解答:已知:物体的重力为G=200N,手拉绳的力是F=150N,n=2
求:滑轮的机械效率η=?
解:滑轮的机械效率:
η=
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/4.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/5.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/6.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/7.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/8.png)
答:滑轮的机械效率为66.7%.
点评:此题考查了滑轮组的特点和机械效率计算公式及其变形的应用,需要熟练掌握基本规律,知道机械效率的变形公式η=
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/9.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/10.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/11.png)
![](http://thumb.1010pic.com/pic6/res/czwl/web/STSource/20131104181732439413501/SYS201311041817324394135020_DA/12.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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