问题
填空题
一个做匀加速直线运动的物体，其位移与时间关系是，x和t的单位分别是m和s，则物体的加速度为（），它从开始运动到速度变为零所经历的时间为（）
答案
参考答案：-6 m/s2；3
解析：
加速度为位移对时间的二次导数，故由
可知加速度为-6 m/s²，速度为位移对时间的导数，故有速度
，它从开始运动到速度变为零所经历的时间为3秒。
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一个做匀加速直线运动的物体，其位移与时间关系是，x和t的单位分别是m和s，则物体的加速度为（），它从开始运动到速度变为零所经历的时间为（）
参考答案：-6 m/s2；3
解析：
加速度为位移对时间的二次导数，故由可知加速度为-6 m/s²，速度为位移对时间的导数，故有速度，它从开始运动到速度变为零所经历的时间为3秒。
| 完型填空。 |
| Mr Cross wanted to go to his hometown 1 . He liked to sit beside a window when he was flying. So he 2 a window seat when he got in the plane. He found that all of them were taken 3 one. There was a soldier sitting in the seat beside this one and Mr Cross was happy that the soldier had not 4 the one by the window. When he 5 it, Mr Cross saw that there was a piece of paper 6 some words on the seat. It said, "This seat is broken. You can't take it, Thank you." "A broken seat in a plane? Is that 7 ?" Mr Cross said 8 , but he walked on and found 9 empty seat, not beside a window, to sit in. When the plane was quite 10 , a very beautiful girl got into the plane. As soon as he saw her, the soldier quickly took the paper off the seat beside his and let the girl sit in during the whole trip. |
| ( )1. A. by bus ( )2. A. found out ( )3. A. only ( )4. A. sat ( )5. A. reached ( )6. A. and ( )7. A. good ( )8. A. loudly ( )9. A. other ( )10. A. fast | B. by ship B. found B. on B. taken B. arrived B. with B. comfortable B. happily B. others B. rushed | C. by train C. looked for C. except C. put C. saw C. for C. dangerous C. to the soldier C. another C. crowded | D. by air D. looked D. to D. seen D. got D. of D. possible D. to himself D. the other D. full |