问题 填空题

大型载重汽车下坡时间较长时,为防止刹车片过热造成刹车失灵,要向刹车片和轮胎喷水降温.刹车片过热是通过       方式增加内能的;水喷到刹车片上时,看到热气腾腾,是利用水的     (填一种物态变化名称)过程吸热,来降低刹车片的温度.

答案

做功,汽化

题目分析:改变物体的内能有做功和热传递两种方式,做功是能量的转化过程,热传递是能量的转移过程,二者改变内能是等效的。本题中的问题是“刹车片过热”,过热的原因是刹车的过程中刹车片与轮胎摩擦生热,机械能转化为内能,是通过做功的方式增加内能。水喷到刹车片上时,水吸收热量,温度升高变成水蒸气,是利用水的汽化过程吸热,来降低刹车片的温度。

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My problem is my parents. They never stop going on about how I should keep my room tidy, keep my hair tidy and wear smart clothes. They even make me do the washing-up after dinner every night! What should I do?
Helen, USA
My best friend has suddenly become an ex-friend and I don’t know why! Last week we phoned each other every day and emailed too. But at school on Monday she didn’t look at me or speak to me. I don’t know what I’ve done.
Gimbya, India
Hi, Helen. I think you should do what your parents ask. You should respect them. It’s their house you live in and their money you spend.
Emily, New Zealand
Why do you think you’re the only one with parents like that? All parents are the same. They don’t understand that fashions have changed in the last 30 years! Tom, America
I feel sorry for you, Gimbya. My best friend did the same to me and I still don’t know the reason. Could you ask another friend to speak to her for you?
George, France
Helen, why should your parents do all the housework? You should help around the house. I think it’s OK for students to wear school uniforms. Teenagers should look like teenagers.
Simon, Scotland
Don’t worry about it so much! Phone your friend up as usual and she won’t be able to ignore(忽视) you. Everything will be fine.
Aisha, Nigeria
 
45. Helen’s problem is about her ______.
A. classmates             B. study            C. parents           D. room
46. ______ has the same problem as Gimbya.
A. George              B. Aisha             C. Helen                  D. Ali
47. ______ don’t agree with Helen. They think she should change her idea.
A. Tom and Emily                                 B. Emily and Simon                          
C. Simon and Tom                              D. Aisha and George
48. An ex-friend is a person who is ______.
A. gets along well with others
B. quite helpful when you have any problem
C. ready for asking you for help all the time
D. no longer a good friend as before