跳起摸高是中学生进行的一项体育活动，某同学身高1.80m，质量65kg，站立举手达到2.20m，此同学用力蹬地，经0.45s竖直离地跳起，设他蹬地的力的大小恒定为1060N，计算他跳起可摸到的高度．（g=10m/s2）
设人离地时获得速度为v，据动量定理有：（F-mg）t=mv
由竖直上抛运动公式得：h=v2 2g
由上述两式解得：h=0.4m
所以该同学摸高为：H=2.2+0.4=2.6m．
答：他跳起时可摸到的高度为2.6m
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| I am a people watcher, a trait magnified when I travel. On the train to and from Tokyo, I realized, 1 , that my fellow riders who were Japanese rarely 2 up and around or used their eyes to interact with other people. This 3 me at first. To my American mind such interaction has the 4 of mutual (相互的) acknowledgement. But then I remembered 5 that the Japanese rarely maintain direct eye contact. Perhaps my people watching seemed 6 . I tried to be more subtle (细心的). I had also read how the Japanese feel 7 to each other as a group by a sense of responsibility. 8 , as a Caucasian Westerner, I was obviously an outsider, I often 9 being a temporary member of the group. Once, sitting at a long stop of a local train, I 10 as several people got up and left the car when a faster train to their 11 pulled into the station. It was cold outside and every person 12 to press the "CLOSE" button as they exited the train doors to help keep out the cold air for the group 13onboard. I always feel a bit embarrassed at having the unearned good fortune of being a 14 speaker of the language. In Japan I was 15 for the many kind strangers who were willing to use their English to 16 me. And in a country where the Roman alphabet is not used in the local language, the abundant English signage was 17 aimed at helping travelers. For the most part on this trip, I found that I was left alone until I asked for help.I 18 little curiosity or interest in interacting with me. When I entered a restaurant or shop, I felt I was 19 as a local resident would be. Welcome is the greeting often shouted out 20 by the staff when customers enter restaurants or stores. | ||||
| ( )1. A. however ( )2. A. looked ( )3. A. surprised ( )4. A. character ( )5. A. reading ( )6. A. polite ( )7. A. upset ( )8. A. As though ( )9. A. benefited from ( )10. A. observed ( )11. A. home ( )12. A. made sure ( )13. A. come ( )14. A. foreign ( )15. A. thankful ( )16. A. hit ( )17. A. obviously ( )18. A. realized ( )19. A. welcomed ( )20. A. coldly | B. though B. noticed B. satisfied B. nature B. seeing B. gentle B. separated B. Even though B. took from B. recognized B. destination B. promised B. left B. national B. appreciative B. call B. specially B. sensed B. loved B. warmly | C. yet C. discovered C. puzzled C. moral C. thinking C. rude C. lonely C. Though C. got from C. found C. office C. wished C. remained C. native C. hateful C. help C. particularly C. felt C. arranged C. hearty | D. therefore D. wandered D. wondered D. quality D. understanding D. noble D. connected D. Unless D. moved from D. watched D. company D. guarantee D. stood D. natural D. grateful D. hurt D. clearly D. knew D. treated D. kindly | |