题目内容
(12分) 如图所示,粗糙程度均匀的绝缘斜面倾角为θ。其下方O点处有一固定的正点电荷,电荷量为Q,OD⊥MN,OM=ON,质量为m、带负电的小滑块以初速度v1从M点沿斜面上滑,到达N点时速度恰好为零,然后又滑回到M点,速度大小变为v2。若小滑块带电量大小为q且保持不变,可视为点电荷。求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031442314980.jpg)
(1)N点的高度h;
(2)若小滑块向上滑至D点处加速度大小为a,求小滑块与斜面间的摩擦因数μ。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031442314980.jpg)
(1)N点的高度h;
(2)若小滑块向上滑至D点处加速度大小为a,求小滑块与斜面间的摩擦因数μ。
(1)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031443242086.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003144293774.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031443242086.png)
试题分析:(1)设小物块从M到N或N到M过程摩擦力做的功大小为Wf
M和N在到点电荷距离相等即在同一个等势面上,所以电场力不做功,根据动能定理有
M到N:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031443401110.png)
N到M:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031443551097.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003144293774.png)
根据几何关系有
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031444022370.png)
经过O点,电场力与斜面垂直,沿斜面方向有
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031444181097.png)
垂直斜面方向
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031444331454.png)
滑动摩擦力
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003144621570.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250031446363497.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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