在匀速水平前行的车厢内悬吊一个自由摆动的单摆，如图17所示。忽略空气阻力，则相对于车厢参照系，小球和地球组成的系统机械能是否守恒？()http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/19460be50d0d48a6b4594a4af7cf7b71.png
举一反三
- 在匀速水平前行的车厢里悬吊一个自由摆动的单摆。忽略空气阻力，则相对于车厢参考系，小球和地球组成的系统机械能守恒。但相对于地面参考系，小球和地球组成的系统机械能不守恒
- 船A重P<sub>A</sub>，以速度 <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/1e6a475774084108a4d9ded2c70e6ca1.png" />航行。重P<sub>B</sub>的物体B以相对于船的速度<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/b39c5c7163f846e8bc34287ec16ef1a7.png" />空投到船上，<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/20f0fb6f6dbc40638b69c7a33e96fd41.png" />设与水平面成<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/3651093fa407458596d5b85ce9b1dc5d.png" />角，且与<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/14fe1be64d75470c8843680bac3209a7.png" />在同一铅直平面内。若不计水的阻力，则二者共同的水平速度为____________。<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201812/9456cc95f694413584344f4bad82d008.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/910e6572478f418c97aa55ae3e71eb87.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/eb921b41a733425c811ac7b3848f3afe.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/06d430260f9c402eaf641a0ba96427c5.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/4c6f547166aa4497b9c6e8ff20fb5407.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"/>
- 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"/>
- 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（）<img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/cac36f4b3a2e44ad995e1bee18ebf01a.png" /> A: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/06d8f8a52abb4c43a15a72ec677df441.png" /> B: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/93ab24db77c44423887f27660cbddba6.png" /> C: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/1569ffa699bf4c09a768018b18affffc.png" /> D: <img src="http://image.zhihuishu.com/zhs/onlineexam/ueditor/201901/80becea6e96445f0b2938ab60e7720df.png" />