题目内容
如图所示,足够大的绝缘水平面上有一质量为m、电荷量为-q的小物块(视为质点),从A点以初速度
水平向右运动,物块与水平面问的动摩擦因数为μ。在距离A点L处有一宽度为L的匀强电场区,电场强度方向水平向右,已知重力加速度为g,场强大小为
。则下列说法正确的是 ( )
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082413093690324006.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130936810249.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130936841597.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082413093690324006.png)
A.适当选取初速度![]() |
B.无论怎样选择初速度![]() |
C.若小物块能穿过电场区域,小物块在穿过电场区的过程中,电场力做功为![]() |
D.要使小物块进入电场区,初速度![]() ![]() |
BCD
因为小物块所受电场力
所以无论怎样选择初速度
,小物块都不可能静止在电场区内,A错,B对。小物块带负电所受电场力跟场强方向相反,则穿过电场区电场力做负功为
,C对,刚好穿过电场区的条件
所以要使小物块进入电场区,初速度
的大小应大于
,D对
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130937153589.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130936810249.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130937215534.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241309372471002.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130936810249.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824130937106429.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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