（15分）如图所示，一个质量为m=1．2×10-3kg的小球带电荷量为q=3．0×10-5C的正电，用长度L=1．0m的细线悬挂于固定点O上，此装置置于水平向右的匀强电场中，场强的大小E=3．0×102N/C，现将带电小球拉至O点右侧，使悬线伸直并保持水平，然后由静止释放小球。（g取10m/s2）
（1）求小
球运动到最低点时的动能？
（2）求小球运动到最低点时绳的拉力为多大？
（1）3×10-4（J）（2）1．8×10
-2（N）
根据动能定理：释放点作为初位置，最低点作为末位置，小球在运动的过程中有两个力做功（电场力及重力）
（1）WG＋W重=EK末－EK初 （4分）
mgL-qEL= EK末－0
Ek末= （mg－qE）L
= （1．2×10-3N－0．9×10-3N）×1m
=3×10-4（J） （4分）
（2）在最低点对小球受力分析
Eh=1×10-3 
（3分）
=1．8×10-2（N）
| 完形填空。 | |||
| When I became an amputee at age 29, I was forced to rethink the idea of physical perfection. My life became different, as I changed from an acceptably attractive woman to an object of pity and 1 . Too busy 2 physical pain and obvious mobility limitation, I was not aware of this change at first. I was determined to 3 , feeling good about the progress I had made, as I moved forward. 4 , as I made my first excursion outside the hospital, society had already assigned me a new status. Happy to be free of my restriction in the hospital, I rolled through the shopping mall - a 5 survivor, feeling like a war hero. Unfortunately, I had a rude 6 as I discovered that others did not view me in the way I had come to view myself. All eyes were upon me, yet no one dared to make eye contact. Their efforts to 7 my eyes forced me to realize they saw only my missing legs. Mothers 8 held their children closer as I passed. Elderly women patted me on the head saying, "God Bless You!" with 9 in their eyes. While I sat thinking about what had happened, a small girl came up to me. She stared with unembarrassed 10 at the empty pants. Finding nothing there, she looked up at me with a puzzled look, she innocently asked, "Lady, where did your legs go?" I explained that my legs had been sick. Since my legs hadn't been strong and healthy like hers, the doctors had to 11 them. Leaning her head upwards, she asked, "Did they go to 'Leg Heaven'?" That incident made me think about how 12 children and adults react to the unknown. To a child, an odd appearance is an interesting curiosity and a 13 learning experience while adults often view the same thing with fear and horror. I began to realize that, I, too had been 14 of the same inappropriate reactions before I knew what life was like for an amputee. To fulfill the wholeness of my mind and spirit, I now smile warmly, make eye contact, and speak in a confident manner. By using a 15 approach, I attempt to enlighten society about the fact that having a not-so-perfect body doesn't mean having a poor quality of life. | |||
| ( )1. A. comfort ( )2. A. crying with ( )3. A. endure ( )4. A. Instead ( )5. A. calm ( )6. A. awakening ( )7. A. turn ( )8. A. softly ( )9. A. pity ( )10. A. curiosity ( )11. A. lose ( )12. A. differently ( )13. A. painful ( )14. A. conscious ( )15. A. creative | B. fear B. figuring out B. quit B. Moreover B. poor B. ending B. hold B. protectively B. anger B. determination B. adjust B. positively B. potential B. guilty B. flexible | C. hatred C. holding back C. revenge C. However C. proud C. happening C. catch C. reluctantly C. depression C. enthusiasm C. remove C. strangely C. similar C. ignorant C. positive | D. sadness D. dealing with D. succeed D. Therefore D. rare D. proceeding D. avoid D. pleasantly D. upset D. satisfaction D. stretch D. sympathetically D. common D. short D. scientific |