问题
选择题
在竖直平面内固定一半径为R的金属细圆环，质量为m的金属小球（视为质点）通过长为L的绝缘细线悬挂在圆环的最高点。当圆环、小球都带有相同的电荷量Q（未知）时，发现小球在垂直圆环平面的对称轴上处于平衡状态，如图所示。已知静电力常量为k。则下列说法中正确的是
A．电荷量
B．电荷量
C．绳对小球的拉力
D．绳对小球的拉力
答案
A
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在竖直平面内固定一半径为R的金属细圆环，质量为m的金属小球（视为质点）通过长为L的绝缘细线悬挂在圆环的最高点。当圆环、小球都带有相同的电荷量Q（未知）时，发现小球在垂直圆环平面的对称轴上处于平衡状态，如图所示。已知静电力常量为k。则下列说法中正确的是
A．电荷量
B．电荷量
C．绳对小球的拉力
D．绳对小球的拉力
A
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| John and I were on our way to St. Louis, Missouri, for a quick trip of job interviews. His job 1 him to move, and, even 2 we weren't engaged yet, he asked me to move with him. We had discussed getting married and already looked at 3 . John even asked my parents 4 their blessing. Everything was set, though we weren't officially engaged. As we 5 our plane, we found our seats and we sat waiting for departure. I noticed one of the 6 leave the plane. When he returned we were ready for the plane to 7 . The captain made the usual 8 : altitude(高度), weather, arrival time, my name. What? Did I just hear my name? My heart started 9 heavily. Did I do something 10 ? Even with all of these thoughts racing through my mind, I somehow(不管怎么说) heard every word: " Attention please. Lynette, John Helms would like to know 11 you would spend the rest of your life with him. If you accept, please 12 the 'call' button 13 the attendants(服务员) will be with you shortly." My eyes filled with tears. When John opened a small ring box and smiled, I 14 . "Yes." He placed the ring on my hand and we embraced(拥抱) as the other passengers 15 . I was 16 to push the call button. But I couldn't reach it with my seatbelt(安全带) still fastened, so John gladly pressed it for me. All three attendants 17 , one carrying a bottle of champagne(香槟). As we landed and approached out gate, the 18 again included us in his announcements. "Congratulations to the newly engaged couple. On behalf of(代表) the entire crew , let me wish you the best." John thanked the flight attendants for helping with his plan. It was then 19 we learned that the pilot had left the plane earlier to get the bottle of 20 for us! | ||||
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