略去质量的弹簧原长为2L，刚度为k，两端固定并处于水平位置，在弹簧中点挂一重物，则重物下降x路程中弹性力所作的功为________。
A:
B:
C:
D:
A:
B:
C:
D:
举一反三
- 拉普拉斯（Laplace）方程的表达式为（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/26731bcad75f41389448b29292940653.jpg" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/40e7e55a72ee44f59b45d20c84ebe3a6.jpg" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/c65a79ea4d754174b99f34020d6e1735.jpg" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/139e8d3dc37941549e7b6b1731243172.jpg" />
- 图示单元体应力状态，沿x方向的线应变εx可表示为（ ）。 <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/9fdd7efe625f4047bb61ef38f5aea871.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/5da2d36f7ef84cbc8396b1e27b775bf4.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/164a3d85fdb6462696d83d62b92b2435.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/9e37e58e1c12442e8e018c0af637dfdf.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/41fd81417e5f47bea1db35fed7c2c44e.png" />
- 平面一维稳定渗流的压力分布公式为（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/d08348f3b84f442d87994311dc13686b.jpg" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/2df214c86c5e4103897ba81ce2c6cd98.jpg" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/cc98e4a778cc463c965ac8115e028f86.jpg" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/bc82177c19d44acfa1b365c3d66ed0a4.jpg" />
- 下列四种产品中，（）属于主体附加。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/7de8bb1790ee4eccbc8fe23d663cb293.JPG" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/9f76d9ce04cb4729b4739bdd64d5917b.JPG" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/b4d8b1ab0b9c4f5e8d165f7afd487e00.JPG" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/4862f4e33e114c63bcfa3ebf5c112cba.JPG" />
- 下列四种产品中，（）属于同类组合。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/ee5cc627e4a243ea8fc5025d6736de65.JPG" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/95326815255349e7bb11324655294818.JPG" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/07ebf5a3e62b47d2be75f2574f2bee3e.JPG" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/a46447046f5340d8977c1ffed9a70772.JPG" />