题目

如图所示，a、b、c是北斗卫星导航系统中的3颗卫星，下列说法正确的是（ ）A. b、c的线速度大小相等，且小于a的线速度B. b、c的向心加速度大小相等，且大于a的向心加速度C. c加速可追上同一轨道上的b，b减速可等候同一轨道上的cD. a卫星由于受稀薄气体阻力原因，轨道半径缓慢减小，其线速度也减小 答案：【答案】A【解析】试题分析：卫星绕地球做圆周运动时，万有引力提供圆周运动的向心力，据此讨论卫星做圆周运动时线速度、向心加速度与半径大小的关系，知道做圆周运动的卫星突然加速时会做离心运动而抬升轨道解：卫星运动时万有引力提供圆周运动向心力有：知：A、卫星的线速度知，卫星bc轨There was once a lonely girl who longed so much for love. One day while she was walking in the woods she found two starving birds 1. . She cared them with love and the birds grew strong. Every morning they greeted her with a wonderful song. The girl felt the great love from the birds.2. . The larger and the stronger of the two birds flew from the cage. The girl was so frightened that he would fly away. As he flew close, she grasped him wildly. Her heart felt glad at her success in capturing him. 3. . She opened her hand and stared in horror at the dead bird. Her desperate love had killed him.She noticed the other bird moving back and forth on the edge of the cage. She could feel his great need for freedom. He needed to fly into the clear, blue sky. 4. . The bird circled once, twice, three times.The girl watched delightedly at the bird’s enjoyment. 5. . She wanted the bird to be happy. Suddenly the bird flew closer and landed softly on her shoulder. It sang the sweetest songs that she had ever heard.The fastest way to lose love is to hold on it too tight, while the best way to keep love is to give it wings!A. She gave them some delicious food and left.B. Suddenly she felt the bird go softly.C. Her heart was no longer concerned with her loss.D. One day she left with the two birds at home alone.E. She took them home and put them in a small cage.F. One day the girl left the door of the cage open.G. She lifted him from the cage and threw him softly into the air.