题目内容
(19分)如图,足够长斜面倾角θ=30°,斜面上OA段光滑,A点下方粗糙且
。水平面上足够长OB段粗糙且μ2=0.5,B点右侧水平面光滑。OB之间有与水平方向β(β已知)斜向右上方的匀强电场E=
×105V/m。可视为质点的小物体C、D质量分别为mC=4kg,mD=1kg,D带电q= +1×10-4C,用轻质细线通过光滑滑轮连在一起,分别放在斜面及水平面上的P和Q点由静止释放,B、Q间距离d=1m,A、P间距离为2d,细绳与滑轮之间的摩擦不计。(sinβ=
,cosβ=
,g=10m/s2),求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500395945312309.png)
(1)物体C第一次运动到A点时的重力的功率;
(2)物块D运动过程中电势能变化量的最大值;
(3)物体C第一次经过A到第二次经过A的时间t。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959375617.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959391352.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959407423.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959422510.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500395945312309.png)
(1)物体C第一次运动到A点时的重力的功率;
(2)物块D运动过程中电势能变化量的最大值;
(3)物体C第一次经过A到第二次经过A的时间t。
(1)40W;(2)50J;1.82s;
试题分析:(1)对D进入电场受务分析可得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959485842.png)
设C物体到A点速度为v0,由题知释放后C物将沿斜面下滑,C物从P到A过程,对CD系统由动能定理得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250039595001765.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959516583.png)
故:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250039595311115.png)
(2)由题意,C经过A点后将减速下滑至速度为0后又加速上滑,设其加速度大小为a1,向下运动的时间为t1,发生的位移为x1,对物体C:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250039595471135.png)
对物体D:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959563953.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959578554.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959594668.png)
D从开始运动到最左端过程中:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250039596091262.png)
所以电势能变化量的最大值为50J
(3)设物体C后再加速上滑到A的过程中,加速度大小为a2,时间为t2,对物体C有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250039596251131.png)
对物体D:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959656965.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959672695.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825003959687457.png)
联立并代入数据解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250039599061102.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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