如右图所示,a、b、c是地球大气层外圆形轨道上运行的三颗人造地球卫星,a、b质量相同,且小于c的质量,则( )
A．b所需向心力最大;
B．b、c周期相等,且小于a的周期.
C．b、c向心加速度相等,且大于a的向心加速度;
D．b、c的线速度大小相等,且小于a的线速度.
答案：D
由向心力
，
，
所以
所以A错误；
由
得：
（M为地球质量）
因为
则
所以B错误；
由
得
，则
于是C错误；
，则
，，所以
于是D正确。
| 阅读理解。 | ||||||
| Shakespeare's Birthplace and Exhibition of Shakespeare's World Welcome to the world-famous house where William Shakespeare was born in l564 and where he grew up. The property (房产) remained in the ownership of Shakespeare's family until 1806. The House has welcomed visitors traveling from all over the world, for over 250 years.
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| 1. How much is the admission for a family of two grown-ups and two children? | ||||||
[ ] | ||||||
| A. ￡9.80. B. ￡12.00. C. ￡14.20. D. ￡16.40. | ||||||
| 2. Where is the nearest parking place to Shakespeare's Birthplace? | ||||||
[ ] | ||||||
| A. Behind the exhibition hall. B. Opposite the Visitors' Centre. C. At Windsor Street. D. Near the Coffee House. | ||||||
| 3. A wheelchair user may need help to enter _____. | ||||||
[ ] | ||||||
| A. the House B. the garden C. the Visitors' Centre D. the exhibition hall |