题目内容
(18分)如图甲所示,物块A、B的质量分别是mA=" 4.0kg" 和mB= 3.0kg,用轻弹簧栓接相连放在光滑的水平地面上,物块B右侧与竖直墙相接触.另有一物块C从t =0时以一定速度向右运动,在t =" 4" s 时与物块A相碰,并立即与A粘在一起不再分开.物块C的v-t 图象如图乙所示.求:
(1)物块C的质量mC;
(2)墙壁对物块B的弹力在4 s 到12 s 的时间内对B做的功W及对B的冲量I的大小和方向;
(3)B离开墙后的过程中弹簧具有的最大弹性势能EP.![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241211006883942.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241211007044681.jpg)
(1)物块C的质量mC;
(2)墙壁对物块B的弹力在4 s 到12 s 的时间内对B做的功W及对B的冲量I的大小和方向;
(3)B离开墙后的过程中弹簧具有的最大弹性势能EP.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241211006883942.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241211007044681.jpg)
(1)
=2㎏
(2)I = -36NS,方向向左
(3)
=9J
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121100720331.gif)
(2)I = -36NS,方向向左
(3)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121100735227.gif)
(1)由图知,C与A碰前速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121100766199.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121100766205.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121100798588.gif)
得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121100720331.gif)
(2)墙对物体B不做功,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121100829375.gif)
由图知,12s末A和C的速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121100829202.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121100844732.gif)
得I = -36NS……2分
方向向左……1分
(3)12s末B离开墙壁,之后A、B、C及弹簧组成的系统动量和机械能守恒,且当AC与B速度v4相等时弹簧弹性势能最大.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121100860780.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241211008761055.gif)
得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824121100735227.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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