如图26所示，一根长为l，质量为m的均匀链条，开始时上端悬挂着，下端刚好与平台接触，链子放开自由下落，则当链子下落s距离时，dt时间内落到地面的小段链条作用于平台的力为（）
A:
B:
C:
D:
A:
B:
C:
D:
举一反三
- What are the comedies of Shakespeare? A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/1882addb95d34f3e877db8ec62e82507.png"/> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/4e230d2e03cc46c2b717155e90fdd081.png"/> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/7f4368645eff4e4b9ec89b237843dabd.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/5ccbfc9718084d318abfbbe254ae048b.png"/>
- Which one is Homer’s epic? A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/60a09e42c1cb4c988adcf2fa43a2170c.png"> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/148a547a82cd4f5482de272b09415b7f.png"> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/bc77b52b6ae747fda43ef56a09994b9f.png"> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/9a18e23e6d9a453ea18eaabd88d99376.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" />
- What are the “Four Great Tragedies” of Shakespeare? A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/bf2842136acc4afba0ab8f98320c7d00.png"/> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/ac6493ebe0b44370ac61898fa86c032b.png"/> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/b34e70254de6499eb4641abf0415463b.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/5a8ed85351f948a393c0aca57418e72a.png"/>
- 下列化合物中，能溶于NaOH溶液的是（ ）。 A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/0ac13ea00784450e883eb9c03410a782.png"/> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/a4b0ca2616834826bc2dd7bc22eff5f8.png"/> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/931013ec85074585881d2056a2f28f4b.png"/> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/74e1d5e80d734881a82b75db1b7e02fb.png"/>