题目内容
)如图11所示,倾角30°的光滑斜面上,并排放着质量分别是mA=10kg和mB=2kg的A、B两物块,一个劲度系数k=400N/m的轻弹簧一端与物块B相连,另一端与固定挡板相连,整个系统处于静止状态,现对A施加一沿斜面向上的力F,使物块A沿斜面向上作匀加速运动,已知力F在前0.2s内为变力,0.2s后为恒力,g取10m/s2,求F的最大值和最小值。![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153314771574.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241153314771574.gif)
最大值为100N,最小值为60N,
未施加力时两物体处于平衡状态,则
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331493699.gif)
由题意可知在0.2s末时刻B对A的作用力为零,则:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331509466.gif)
对B由牛顿第二定律得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331524778.gif)
联立以上三式得:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331540424.gif)
以AB整体为研究对象,由牛顿第二定律得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331555948.gif)
即![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331571808.gif)
当
时,
;
当
时,
。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331493699.gif)
由题意可知在0.2s末时刻B对A的作用力为零,则:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331509466.gif)
对B由牛顿第二定律得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331524778.gif)
联立以上三式得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331540424.gif)
以AB整体为研究对象,由牛顿第二定律得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331555948.gif)
即
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331571808.gif)
当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331587499.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331602482.gif)
当
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331633528.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824115331633502.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目