题目内容
质量为4kg的雪橇在倾角
=37°的足够长斜坡上向下滑动,所受的空气阻力与速度成正比,比例系数K未知,今测得雪橇运动的v—t图象如图曲线AD所示,且AB是曲线最左端A点的切线,B点的坐标为(4,15),平行于ot轴的CD线是曲线的渐近线。已知sin37°=0.6,g=l0m/s2。试问:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500462354210329.png)
(1)物体在开始计时的一段时间里做什么性质的运动?最终做什么运动?
(2)当vo =5m/s和v1="10" m/s时,物体的加速度各是多少?
(3)空气阻力系数k及雪橇与斜坡间的动摩擦因数各是多少?
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004623526297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500462354210329.png)
(1)物体在开始计时的一段时间里做什么性质的运动?最终做什么运动?
(2)当vo =5m/s和v1="10" m/s时,物体的加速度各是多少?
(3)空气阻力系数k及雪橇与斜坡间的动摩擦因数各是多少?
(1)见解析;(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004623557716.png)
;(3)
,![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004623604557.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004623557716.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004623573400.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004623588582.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004623604557.png)
试题分析:(1)物体开始时做加速度减小的加速直线运动,最后作匀速运动 (4分)
(2)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004623635974.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004623573400.png)
(3)开始加速时:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250046236661100.png)
最后匀速时
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250046236821015.png)
由①②联立得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004623698713.png)
解得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250046237291357.png)
由②式得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250046237441988.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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