题目内容
如图所示,横截面积S=10
的圆筒上、下部均与大气相通,竖直固定在水平地面上,活塞A与B将一定质量的空气封闭在圆筒中部,活塞A质量
=1kg,活塞B用一轻弹簧与地面相连,弹簧劲度系数k=1000N/m,当活塞处于平衡状态时,被封闭气体长度
=16cm.现用一恒力F将活塞A向上拉,当两活塞重新平衡时,活塞B向上移动了3cm.已知大气压强
=1.0×
Pa,不计活塞与筒壁摩擦.求拉力F的大小及活塞A上移距离ΔL(此过程中温度保持不变).
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201359361881.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120135749969.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120135858960.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120135889948.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120135905952.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120135921961.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201359361881.gif)
30N , 9cm
力F作用前对系统有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201359521167.gif)
力F作用后对系统有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201359671189.gif)
∴ F=k(
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120135983992.gif)
力F作用前对活塞A:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201359991143.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201360771147.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120135921961.gif)
力F作用后对活塞A:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120136170976.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201361861064.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201362011185.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824120135921961.gif)
对气体:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201362481102.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201362641105.gif)
则活塞 A上移距离
ΔL=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241201362791107.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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