某校五楼寝室，学生熄灯就寝后，一同学违规点蜡烛看书，不小心引燃蚊帐，导致火灾．就此事件回答下列问题：

1930年发现，科学家在真空条件下用α粒子轰击 时，产生了一种看不见的、贯穿力很强的不带电粒子，为了弄清楚这是一种什么粒子，人们用它分别去轰击氢原子和氮原子，结果打出一些氢核和氮核，并以此推算出了该粒子的质量，从而确定改粒子为中子．设氢核的质量为m_H，氮核的质量为氢核质量的14倍，碰撞后氢核的速度为v_H，氮核的速度为v_N，假设中子与它们的碰撞为弹性弹性碰撞，碰撞的粒子分别为中子和氢核及中子和氮核．

B

    Hans Christian Andersen was born in Denmark in 1805. He lived with his parents in a town   called Odense. They were a very poor family and they couldn't afford to send Hans Christian to school.

    As a little boy, Hans Christian enjoyed making up fairy tales（童话）and puppet（木偶）shows.

    When he was only eleven years old, his father died and he had to go out to work to make money to help his mother.

    Three years later, Hans Christian left home and went to the city of Copenhagen to be famous and rich. To begin with he didn't do very well there, but at last he was able to go back to school and then on to university to continue his education.

    He wrote fairy tales and stories and soon became famous. At first he wrote the stories that he had heard when he was a child and then began to make up new tales. During his seventy-one year life, Hans Christian wrote over three hundred stories.

    Many of his stories are still enjoyed by children today. Among his best-known stories are: the Emperor's New Clothes, the Ugly Duckling, the Snow Queen, the Princess and the Pea, and the Little Mermaid.