一长木板置于粗糙水平地面上，木板左端放置一小物块，在木板右方有一墙壁，木板右端与墙壁的距离为4.5m，如图（a）所示。t=0时刻开始，小物块与木板一起以共同速度向右运动，直至t=1s时木板与墙壁碰撞（碰撞时间极短）。碰撞前后木板速度大小不变，方向相反；运动过程中小物块始终未离开木板。已知碰撞后1s时间内小物块的v-t图线如图（b）所示。木板的质量是小物块质量的15倍，重力加速度大小g取10m/s²。求

    Ann is a newspaper reporter. She chose this1so she could travel around the world. The work has taught her many unforgettable (令人难忘的) lessons. She has seen wars, earthquakes and death. But she has 2 seen courage, hope and happiness.

    Last year, she won an award for her reporting in Africa. She was very proud 3 it. At first, she thought she got the award because of her good work. But then she realized that she should thank many other people for 4 help.

    Ann was born in Jamaica. Her family was not poor, but it was not 5 , either. Her parents had to 6 hard so that she could go to school. At school, Ann was not a good student, 7 she enjoyed writing because her English teacher said, "Ann, you are a wonderful 8 " The teacher encouraged her all the time.

    Later, Ann went to university in Canada and then 9 a job. It was very difficult. Then, one day, she went to see the editor of a newspaper in Ottawa. The editor gave her a job. "Everyone needs a 10 at first." he said.

美国”9.11”恐怖袭击事件中，毁坏的建筑物散发出大量的石棉，人吸入石棉纤维易患肺癌，石棉是硅酸盐矿物，某种石棉的化学式为：Ca₂Mg_xSi_yO₂₂（OH）₂，该化学式中的x，y的值分别是（　　）