宇宙飞船相对于地面以速度v作匀速直线飞行，某一时刻飞船头部的宇航员向飞船尾部发出一个光讯号，经过△t(飞船上的钟)时间后，被尾部的接收器收到．则由此可知飞船的固有长度为
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举一反三
- 一简谐振动的旋转矢量图如右图，设图中圆的半径为R，则该简谐振动的振动方程为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/dfd995a36f4e4dd2adb52a50cc5a26de.png"/> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/e69d65d5dd4e49f9863425ce3fb5ac54.png"/> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/b13da9634fc9435398489686c8d362f9.png"/> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/e7906edc65b14dc39bafcb683986a690.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/0bfe1b068eac44d59d8772eb9bcbf871.png"/>
- 用波长为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/f83cfabe43504aaabfed8ef51f445118.png" />的光垂直入射在一光栅上, 发现在衍射角为j 处出现缺级, 则此光栅上缝宽的最小值为 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/9f827703044645dcb814a3797bff0686.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/689f4282749d4f79b8c3de619b87d94e.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/7ee1e7c994894f1fb25264c84fbaad9c.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/c72a2486b1304666ad4e18e4614a5f07.png" />
- 《三国演义》第四十九回“七星坛诸葛祭风，三江口周瑜纵火”中，诸葛亮向周瑜提出可借三日三夜东南大风，以助公瑾破曹。诸葛亮借的是哪个风（） A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/7ae07c7288d045048665b872eb883f5b.png"/> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/c2878ab18ac64afd9c5b528efe2c7ed2.png"/> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/e9c5e6054460452c92dadf2ef4093bd4.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201807/9eb59a44e3c44a408835cb05bf3890a6.png"/>
- 一质点在平面上作一般曲线运动，其瞬时速度为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201707/cd2c54e096b2475db8bcecd84e554eb0.png" />，瞬时速率为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201707/359eb2c648264727bd0a2bc72d54b233.png" />，某一时间内的平均速度为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201707/32268b5fc5bc43619f3bb1de9c43715b.png" />，平均速率为<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201707/99f1a21b975449648922aab0accdc025.png" />，它们之间的关系必定有（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201707/27daf7237fe740349eb8756c75d23df6.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201707/f2f418f88e564f8c9d46babbe9bc612b.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201707/5d84042638794095a9b9e7760b0cbb53.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201707/cd811196b38f419c82b27356c7d84ca9.png" />
- <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" />