When a close friend dies, it often forces you to consider your own death. The more you have in common with the friend, the more his death will make you wonder about your own. Sometimes you will naturally say to yourself, "It could just as easily have been me." Such a death has a way of reminding us how fragile life is, and it may cause you to reassess（重新评价） the direction of your own life.
Jack's story is a good example. A successful businessman making a lot of money, Jack didn't spend as much time with his family as he wanted. His job required him to work long hours. But three years ago one of his best friends, a man who worked in the same office, had a heart attack. He died while celebrating his daughter's eighteenth birthday in a restaurant. He was only fifty years old.
Not long after his friend's death, Jack started to have a chest pain. Finally he had a good physical check-up. He received a clean bill of health. But the chest pain continued. He kept thinking of the death of his friend. Jack thought about how much his friend missed in life and he saw how hard it was for his friend's family to manage after he passed away.
Jack realized that he didn't want to end up his life that way. He talked his feelings over with his wife and children, and decided to change his way of life. The family moved to a small town where he started a simple life. Now he is running a small art gallery（画廊）. He is relaxed, and says he has never been so happy in his life, and he has got no more chest pain.
63. Your close friend's death is __________________ to you.
A. a warning B. common C. a direction of life D. an example
64. The underlined sentence in the third paragraph means "________________".
A. The doctor didn't write a word on his bill
B. The doctor didn't want Jack to pay for the bill
C. The doctor didn't find anything wrong with him
D. The doctor didn't want to treat his pain
65. His friend's death made Jack ________________.
A. lose much interest in life
B. realize that he missed the friend very much
C. doubt his way of life
D. ill for some time
66. While living in the small town Jack ________________.
A. earns less money B. gets more time
C. has a happier life D. does all these mentioned above
的滑块静止在水平台面右端
点，另一质量为
的滑块从与
的
点以初速度
以向右运动，至
处静止，
落到地面上
点。已知两滑块均能看成质点，且
，
，
，重力加速度为
，求：
（2）
（3）
做平抛运动，其竖直方向遵守自由落体规律，所以有：
① 解得
与
，
，碰后
。
② （2分）
③ （2分）
④ （1分）
，代入③④求解得：
，
（方向向左） （1分）
，所以有：
⑤
向左做匀减速运动，至
处静止，设其位移为
⑥ （2分） 
的距离为：