题目内容
如图所示,在水平桌面上放一块重为20N的木块A,木块与桌面间的动摩擦因数μA=0.5,
(1) 使这块木块沿桌面作匀速运动时的水平拉力F为多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241626155476160.png)
(2)如果再在木块A上加一块重为10N的木块B,B与A之间的动摩擦因数
=0.2,那么当A、B两木块一起沿桌面匀速滑动时,对木块A的水平拉力应为多大?此时木块B受到木块A的摩擦力多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241626160316640.png)
(3)如果拉力与水平面呈53°角斜向上,那么当A、B两木块一起沿桌面匀速滑动时,对木块A的拉力应为多大?(sin53º=0.8,cos53º=0.6)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241626162187921.png)
(1) 使这块木块沿桌面作匀速运动时的水平拉力F为多大?
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241626155476160.png)
(2)如果再在木块A上加一块重为10N的木块B,B与A之间的动摩擦因数
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162615703368.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241626160316640.png)
(3)如果拉力与水平面呈53°角斜向上,那么当A、B两木块一起沿桌面匀速滑动时,对木块A的拉力应为多大?(sin53º=0.8,cos53º=0.6)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241626162187921.png)
(1)10N(2)15N,0(3)15N
试题分析:(1)当拉力等于木块受到的滑动摩擦力时,木块沿桌面作匀速运动
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241626165151061.png)
(2)当A、B两木块一起沿桌面匀速滑动时,拉力等于木块受到的滑动摩擦力,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241626166861241.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162616889468.png)
(3)x方向:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162617248840.png)
y方向:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241626174041124.png)
联立①②解得F=15N
点评:计算滑动摩擦力时,一定要注意
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162617700597.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824162617841411.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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