题目内容
根据流体力学知识,流体对物体的作用力可用f=αρ0Av2来表达.α为一系数,ρ0为空气密度,A为物体的截面积,v为物体相对于流体的速度.已知地球表面处α=0.5,ρ0=1.25kg/m3,g=10m/s2.球体积公式为V=
π r3.若将沙尘颗粒近似为球形,沙尘颗粒密度ρs=2.8×103kg/m3,半径r=2×10-4m.求:
(1)沙尘颗粒在空气中竖直下落时的最大加速度;
(2)沙尘颗粒在空气中竖直下落时的速度最大值;
(3)地面附近形成扬沙天气的风速至少为多少.
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004830807373.png)
(1)沙尘颗粒在空气中竖直下落时的最大加速度;
(2)沙尘颗粒在空气中竖直下落时的速度最大值;
(3)地面附近形成扬沙天气的风速至少为多少.
(1)
,方向竖直向下(2)
(3)v≥3.46m/s
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004830822551.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004830838634.png)
试题分析:(1)沙尘颗粒刚开始下落速度为零时,
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004830869384.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004830822551.png)
(2)速度最大时加速度为零:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004830900525.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004830916800.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048309311009.png)
则:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250048309631489.png)
(3)当
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825004831025822.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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