根据欧拉观点，矢量b的随体导数可以表示为（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/bd9f6e077ec54badbbc07b69be144aef.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/e6ca2342befc409ebb9baa3e1d3640f0.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/475c4f089d404710afedf2c6dfdd6664.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/685d9b405ede4220a7c0f525d10a7a50.png" />

依据欧拉观点，以下表述恒定流动密度变化率数学表达式正确的是（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/3da5de2eff974c5f85129b3e638b211b.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/4121afc979e24032bb182e14b3e3deb2.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/a798767da3044f19a50cb58e98310999.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/1d5b29a2a7594af098ce2a9bfb01ca3f.png" />

在工程图中，对尺寸标注的前后缀进行修改需要选择哪个图标？( ) A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/151dad8b642a4cd286a5a6f33a379f06.png"/> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/171628c951b44619b4ae9c5afa4f8c5d.png"/> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/dc4e87847b6d41d6ba2f0838528fb898.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/a8ebfd35da454980a8e7e8ebd5ac6abc.png"/>

图示曲柄连杆机构，已知曲柄OA长L，重量不计，连杆AB长2L，重P，受矩为M的力偶和水平力Ｆ的作用，在图示位置平衡。若用虚位移原理求解，则必要的虚位移之间的关系为___________，力F的大小为_____________________。<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/be06434307bd424abfc4ebfe02661f7a.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/b8e7b964d1c84aeca7b22ddef4de87a2.png" />;<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/a584946cde17410c945d6611ff2113b5.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/1aaef24e28ee477ab25dae0a400bf23f.png" />;<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/f3b395453e1d48bdadff2e37dfbbb626.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/be37912822f0451bb15639b7fa0589f1.png" />;<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/6d1112b5c1b4446b93578138388ed79f.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/89b7bcef6b51410cb624a654747d56ee.png" />;<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/0e2b78f437914a1eb8327d13185eaedf.png" />

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