如图所示，摆球质量为m=2kg，悬线的长为L=1m，把悬线拉到水平位置后放手.设在摆球运动过程中空气阻力Ff=2N的大小不变，求摆球从A运动到竖直位置B时，重力mg、绳的拉力FT、空气阻力Ff各做了多少功？g="10" m/s2
-3.14（J）
重力做的功WG=mgh=20J 3分
绳的拉力做的功WN=0 3分
空气阻力做的功Wf=-Ffs=-Ff
=-3.14（J）3分
本题考查的是力做功问题。功等于力和在力的方向上的位移的乘积，关键是分清哪个力对应哪个位移。
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| People often say that the Englishman's home is his castle. They mean that the home is very important and 1 . Most people in Britain live in houses 2 flats, and many people own their homes. This means that they can make them individual; they can 3 them and change them in any way they 4 . In a crowded city the individual knows that he or she has a private space which is 5 for himself of herself and for 6 friends. People usually like to 7 their space. Are you sitting now in your home or in a library or on a beach or a train? If you are on the beach you may have spread your 8 around you; on the train you may have 9 your coat or small bag on the seat beside you; in a library you may have one 10 or chair which is your own. Once I was traveling on a 11 to London. I was in a section for four people and there was a table between us. The man on the 12 side to me had his briefcase on the table. There was no 13 on my side of the table at all. I was made rather 14 , I thought he thought that he owned the 15 table. I took various papers out of my bag and put them on 16 ! When I did this he stiffened and his eyes nearly popped out of his head. I had 17 his space! A few minutes later I t  ook my papers 18 his case in order to read them. He immediately 19 his case to his side of the table. (Of course , it is 20 that he just wanted to be helped to me! ) | |||
| ( )1. A. helpful ( )2. A. rather than ( )3. A. buy ( )4. A. make ( )5. A. only ( )6. A. unwanted ( )7. A. mark ( )8. A. towels ( )9. A. find ( )10. A. book ( )11. A. plane ( )12. A. opposite ( )13. A. matter ( )14. A. angry ( )15. A. right ( )16. A. the table ( )17. A. invaded ( )18. A. into ( )19. A. hid ( )20. A. possible | B. personal B. as well as B. leave B. clear B. already B. close B. decide B. sands B. give B. corner B. train B. back B. weight B. hurt B. only B. his case B. shut B. for B. set B. true | C. necessary C. as a result of C. paint C. like C. ever C. sick C. choose C. papers C. put C. companion C. way C. wrong C. light C. fearful C. small C. the seat C. separated C. off C. moved C. wonderful | D. useful D. or rather D. offer D. prepare D. even D. invited D. keep D. flags D. store D. meal D. street D. good D. space D. busy D. whole D. his side D. shared D. out of D. kept D. ordinary |