题目内容
如图所示,质量为3m、长度为L的木块置于光滑的水平面上,质量为m的子弹以初速度v0水平向右射入木块,穿出木块时速度为
,设子弹受到的阻力始终保持不变.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241345597221925.jpg)
(1)求子弹穿透木块后,木块速度的大小;
(2)求子弹穿透木块的过程中,木块滑行的距离s;
(3)若改将木块固定在水平传送带上,使木块始终以某一恒定速度(小于v0)水平向右运动,子弹仍以初速度v0水平向右射入木块.如果子弹恰能穿透木块,求此过程所经历的时间.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134559659477.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241345597221925.jpg)
(1)求子弹穿透木块后,木块速度的大小;
(2)求子弹穿透木块的过程中,木块滑行的距离s;
(3)若改将木块固定在水平传送带上,使木块始终以某一恒定速度(小于v0)水平向右运动,子弹仍以初速度v0水平向右射入木块.如果子弹恰能穿透木块,求此过程所经历的时间.
(1)
(2)
(3)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134559909754.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134559768467.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134559831474.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134559909754.png)
)解:(1)对子弹和木块系统研究,设木块是速度为v,根据动量守恒定律:
(2分)
得
(2分)
(2)分别对子弹和木块研究,设木块滑行的距离为s,根据动能定理:
(1分)
(1分)
解之得
(2分)
(3)设传送带的速度为u,对子弹研究,根据动量定理和动能定理:
(1分)
(1分)
解之得
(2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134559956846.png)
得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134559768467.png)
(2)分别对子弹和木块研究,设木块滑行的距离为s,根据动能定理:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241346000651265.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134600112804.png)
解之得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134559831474.png)
(3)设传送带的速度为u,对子弹研究,根据动量定理和动能定理:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134600236698.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241346002831121.png)
解之得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824134559909754.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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