题目内容
一辆汽车在恒定的功率牵引下,在平直公路上由静止出发,经4min的时间行驶1.8km,则在4min末汽车的速度( )
A.等于7.5m/s | B.大于7.5m/s | C.等于15m/s | D.15m/s |
BD
汽车在恒定功率下由静止启动是加速度越来越小的变加速运动,很难通过运动方程求瞬时速度,一般的方法是由动能定理求出动能、再求速度但这必须要知道牵引力、阻力所做的功。而现在这些条件都未知,但在恒定功率下,其4min内的平均速度
,由于加速度变小,所以末速度
,同时由于位移关系
,其
图象如图,为一上凸的曲线。打斜线部分“面积”相等,即位移为
,如果
,则位移
;而
则位移
,故
,正确选项是BD。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241137513263452.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113751139522.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113751155254.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113751170278.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113751186215.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113751201624.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113751233445.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113751248435.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113751264439.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113751248435.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824113751311591.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241137513263452.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
练习册系列答案
相关题目