设地球的半径为R0，质量为m的卫星在距地面2R0高处做匀速圆周运动，地面的重力加速度为g，则下列说法正确的是（ ）
A．卫星的线速度为gR0 2
B．卫星的角速度为g 8R0
C．卫星的加速度为g 2
D．卫星的周期为2π2 7R 0 g
A、研究卫星绕地球做匀速圆周运动，根据万有引力提供向心力，列出等式：
=mGmM r2
，v2 r
解得：v=
其中r=3R0 ①GM r
忽略地球自转的影响，根据万有引力等于重力列出等式：
=mg，GmM R 20
解得：GM=gR02 ②
由①②得：卫星的速度大小v=
，故A错误gR0 3
B、卫星的角速度ω=
=v r
，故B错误g 27R0
C、根据圆周运动知识得：a=
=v2 r
，故C错误g 9
D、卫星的周期T=
=2π2πr v
，故D正确2 7R 0 g
故选D．
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| The family had just moved. The young woman was feeling a little 1 . It was Mother's Day - and she was 800 miles away from her parents. She had called them that morning, and her mother had 2 how colorful their backyard was 3 spring had arrived. Later, she told her husband how she 4 those lilacs (丁香) in her parents' yard. "I know where we can find some," he said. "Get the 5 and come on." So off they went. Some time later, they stopped at a hill and there were lilacs all round. The young woman rushed up to the nearest 6 and buried her face in the flowers. Carefully, she 7 some. Finally, they returned to their car for the 8 home. The woman sat smiling, surrounded by her 9 . When they were near home, she shouted "Stop," got off quickly and 10 to a nearby nursing home. She went to the end of the porch (门廊), where a(n) 11 patient was sitting in her wheelchair, and put the flowers into her lap. The two 12 , breaking into laughter now and then. Later the young woman turned and ran back to her 13 . As the car pulled away, the woman in the wheelchai r 14 with a smile, and held the lilacs 15 . "Mom," the kids asked, " 16 did you give her our flowers?" "It is Mother's Day, and she seems so 17 while I have all of you. And anyone would be 18 by flowers." This pleased the kids, but not the husband. The next day he 19 some young lilacs around their yard. I was the husband. Now, every May, our yard is full of lilacs. Every Mother's Day our kids 20 purple lilacs. And every year I remember that smile of the lonely old woman. And that has become a forever touching memory of my life. | ||||
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