题目内容
一个质量为2kg的物体静止在足够大的水平地面上,物体与地面间的动摩擦因数
。从t=0开始,物体受到一个大小和方向呈周期性变化的水平力F的作用,力F 随时间的变化规律如图9所示。重力加速度
, 求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020204192573.png)
(1)0~2s时间内物块运动的加速度
的大小和方向;
(2)
时物块运动的瞬时速度
的大小和方向;
(3)0~6s时间内物块运动的位移的大小和方向。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020388475.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020403610.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020204192573.png)
(1)0~2s时间内物块运动的加速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020435315.png)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020466412.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020481298.png)
(3)0~6s时间内物块运动的位移的大小和方向。
(1)
=2m/s2,加速度
的方向向右;(2)
=4m/s,速度
的方向向右;
(3)x=8.0m方向向右
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020435315.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020435315.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020481298.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020481298.png)
(3)x=8.0m方向向右
试题分析: (1)据牛顿第二定律知:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020575703.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020205911533.png)
加速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020435315.png)
(2)据速度公式有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020622842.png)
速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020481298.png)
(3)0~2s时间内物块运动的位移为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020206691148.png)
2~4s时间内,物块先向右匀减速运动至速度为零,令加速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020684344.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020700327.png)
据牛顿第二定律有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020207151632.png)
方向向左 1分
据速度公式有:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020731597.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020207471073.png)
物体向右匀减速运动的位移:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020207621867.png)
2.8~4s时间内物块将向左静止开始匀加速运动,令加速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020871352.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020208711644.png)
物体向左静止开始匀加速运动的位移:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020209031395.png)
4s时物体的速度:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020918997.png)
4~6s时间内物块先向左匀减速运动,令加速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020918334.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020209491641.png)
令向左匀减速到静止所用时间为
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020965320.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002020981604.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020209961230.png)
向左匀减速运动的位移:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020210271378.png)
之后,4.2s~6s时间内物块从静止开始向右匀加速运动,加速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825002021043681.png)
向右运动的位移:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020210591320.png)
0~6s时间内的总位移:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250020210742098.png)
方向向右。 1分
![](http://thumb2018.1010pic.com/images/loading.gif)
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