题目内容
如图所示,两根细线中的拉力分别为T1、T2,现在使A、B带上同种电荷,此时上下两根细线的拉力分别为T1′、T2′则( )![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_ST/images0.png)
A.T1′=T1,T2′=T2
B.T1′>T1,T2′>T2
C.T1′=T1,T2′>T2
D.T1′<T1,T2′<T2
【答案】分析:A、B始终处于静止状态,分别对带电前后进行受力分析,判断绳子拉力的变化.
解答:解:带电前:对B有:
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/images0.png)
T2=GB
对AB组成的整体有:
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/images1.png)
T1=GA+GB
带电后:对B有:
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/images2.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/0.png)
对整体:
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/images4.png)
T′1=GA+GB
综上所述:
,![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/2.png)
故选:C
点评:处于受力平衡状态的物体在求解或进行大小变化的判断时,只要选好研究对象进行正确的受力分析,应用平衡条件判断即可.
解答:解:带电前:对B有:
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/images0.png)
T2=GB
对AB组成的整体有:
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/images1.png)
T1=GA+GB
带电后:对B有:
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/images2.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/0.png)
对整体:
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/images4.png)
T′1=GA+GB
综上所述:
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/1.png)
![](http://thumb.1010pic.com/pic6/res/gzwl/web/STSource/20131029192159555273273/SYS201310291921595552732002_DA/2.png)
故选:C
点评:处于受力平衡状态的物体在求解或进行大小变化的判断时,只要选好研究对象进行正确的受力分析,应用平衡条件判断即可.
![](http://thumb2018.1010pic.com/images/loading.gif)
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