函数 ，则在上()。http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/3a9941245dbe478a981007f0b8be9a43.png

竖立的圆筒形转笼，半径为R，绕中心轴OO＇转动，物块A紧靠在圆筒的内壁上，物块与圆筒间的摩擦系数为μ，要使物块A不下落，圆筒转动的角速度ω至少应为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/89f0a85f81ed4ec098b93d0d55ce31ba.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/79bff9228f8b44a8a991dc5ea15bd1dc.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/3d95ab9efaf9495eb3dc5095875dcb62.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/72b61163487846fab5c581b986a3e171.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/fc10477bb0e64eea9f0a23717ea615d2.png" />

如图所示，用一斜向上的力<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/2c66b17a89294028b013f78ac88214d8.png" />(与水平成30°角)，将一重为G的木块压靠在竖直壁面上，如果不论用怎样大的力F，都不能使木块向上滑动，则说明木块与壁面间的静摩擦系数m的大小为 <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/dce25bc1a82e4dd996be3f0109b2524a.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/289aa51d07e34d4bb3dfeacd6a1ca096.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/8a557aef21054265b69c406b27e26221.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/e97a8667b31e41439e0cb168a9b4934f.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/facdf89eaa084d3eb7af997874a8ddc0.png" />

已知某四进制数字信号传输系统的信息速率为2400b/s，接收端在半小时内共收到216个错误码元，则该系统的误码率 Pe 等于（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/2c2151442ead41aca212beea9b5956e0.png"> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/360135bdb3ab42ee81e4df00e7d7bc0c.png"> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/dfcc9daeba714b3b9c0397dcad63f706.png"> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/bd125168bb1d4ba1b7bf04dfdf63abc6.png">

曲线的拐点为及（ ）。http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/6439936304844e448e00adcd3574c20e.png