题目内容
如图所示,有一水平放置的圆盘,上面水平放一劲度系数为
的弹簧,弹簧的一端固定于轴
上,另一端连接一质量为
的物体A,物体与盘面间的动摩擦因数为
,开始时弹簧未发生形变,长度为
,设最大静摩擦力等于滑动摩擦力。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241658097962276.jpg)
则:(1)盘的转速n0多大时,物体A开始滑动?
(2)当转速达到2n0时,弹簧的伸长量
是多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165808017320.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165808189300.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165808563346.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165809000306.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165809406310.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241658097962276.jpg)
则:(1)盘的转速n0多大时,物体A开始滑动?
(2)当转速达到2n0时,弹簧的伸长量
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165809811389.png)
(1)
(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241658108411086.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165810295947.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241658108411086.png)
试题分析:若圆盘转速较小,则静摩擦力提供向心力,当圆盘转速较大时,弹力与静摩擦力的合力提供向心力。
(1)当圆盘转速为n0时,A即将开始滑动,此时它所受的最大静摩擦力提供向心力,则有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165811246777.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165811668646.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165810295947.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165810295947.png)
(2)当圆盘转速达到
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165812370451.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165812775960.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165812978714.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824165813493573.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241658108411086.png)
点评:本题难度较小,此题分析出向心力的来源是突破口,当所需的向心力大于受到的摩擦力时开始发生相对滑动,不足的向心力由弹力提供
![](http://thumb2018.1010pic.com/images/loading.gif)
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