2010年2月16日，在加拿大城市温哥华举行的第二十一届冬奥会花样滑冰双人自由滑比赛落下帷幕，中国选手申雪、赵宏博获得冠军．如图所示，赵宏博以自己为转动轴拉着申雪做匀速圆周运动．若赵宏博的转速为30 r/min，手臂与竖直方向的夹角为60°，申雪的质量是50 kg，则下列说法正确的是
A．申雪做圆周运动的角速度为π rad/s
B．申雪做圆周运动的角速度为π/2 rad/s
C．赵宏博手臂拉力约是850 N
D．赵宏博手臂拉力约是1000 N
AD
题目分析：申雪做圆周运动的角速度等于赵宏博转动的角速度．则ω＝30×2π/60 rad/s＝π rad/s，选项A正确；故选项B错误；由Fcos30°＝mrω2，假设半径为2m，解得F＝1000 N，D正确，C错误，故选AD
点评：本题难度较小，掌握圆周运动中各物理量间的关系，此题假设半径大小是关键
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| In the city of Fujisawa, lives a woman named Atsuko Saeki. When she arrived, however, she 1 of going to the United States. Most of what she knew about American 2 was from the textbooks the had read. "I had a 3 in mind: Daddy watching TV in the living room. Mummy 4 cakes and their teenage daughter off to the cinema with her boyfriend." Atsuko 5 to attend college in California. When she arrived, however, she found it was not her 6 world. "People were struggling with problems and often seemed 7 ," she said. "I felt very alone." One of the hardest 8 was physical education. "We played volleyball,"she said. "The other students were 9 it, but I wasn't." One afternoon, the instructor asked Atsuko to 10 the ball to her teammates so they could knock it 11 the net. No problem for most people. But is terrified Atsuko. She was afraid of losing face 12 she failed. A young man. On her team 13 what she was going through. "He walked up to me and 14 ,'Come on, You can do that.'" "You will never understand how those words of 15 . made me feel…Four words…You can do that. I felt like crying with happiness." She made it through the class. Perhaps she thanked the young man; she is not 16 . Six years have passed. Atsuko is back in Japan,working as a salesclerk. "I have 17 forgotten the words," she said. "When things are not going so well, I think of them." She is sure the young man had no idea how much his kindness 18 to her. "He probably doesn't even remember it." she said, That may be the lesson. Whenever you say something to a person―cruel or kind― you have no ides how long the words will 19 . She's all the way over in Japan, but still she hears those four 20 words; You can do that. | ||||
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