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
A:
B:
C:
D:
A:
B:
C:
D:
举一反三
- 波长为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/91ddb92399a343cc990e393ea7ae49e4.png" />的单色光垂直入射于光栅常数为d、缝宽为a、总缝数为N的光栅上。取<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/d02f9b0d40604921bb6eba164d27ae52.png" />，则决定出现主极大的衍射角<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/294d963ff1564c7e9c98a2ca06a7278c.png" />的公式可写成（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/7e2fd47a37564a53afe33f3fadb46a41.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/2c25a6b55e74467992e1b3b1d02662d8.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/f852c846c7b642f6bbcaf2bcfa75c310.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201802/27465a93e5ca42d8a18f9a3222d0e52b.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">
- 图示结构C截面弯矩为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201906/4f75b4fba9ff4be1b04a5e100c86c65e.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201906/145877d7a442497f9fe1266fa394ba2e.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201906/1b6f8295e7bc44b0b8a2bee20e062fc4.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201906/18776e34a7504dfcbe40fbdf73958b14.png" /> D: 0
- <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/2205d9f03e724a04b34f2f1045309079.png" />的幅频响应是，幅频响应是。 A: 1，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/760d7fcc2f264ed1b10fb836cb48f565.png" /> B: -1，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/21f685d2962e4b6993bfcaa513bdbf68.png" /> C: 2，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/57267e995f86426899ce3cc0177a2343.png" /> D: 1，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201903/ea8ba62853a94a15a5620c5165e3594a.png" />