题目内容
将一个小球从报废的矿井口由静止释放后做自由落体运动,4s末落到井底。该小球开始下落后第2s内和第4s内的平均速度之比是 ( )
A.1∶3 | B.2∶4 | C.3∶7 | D.4∶16 |
C
试题分析:根据公式
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160838692436.png)
第1s末小球的速度为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160838817413.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160838973504.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160839238781.png)
第3s末物体的速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160839566500.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160839815471.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160839925815.png)
故
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824160840081573.png)
故选C,
点评:自由落体运动是初速度为零,加速度为g的匀加速直线运动
![](http://thumb2018.1010pic.com/images/loading.gif)
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题目内容
A.1∶3 | B.2∶4 | C.3∶7 | D.4∶16 |