题干

关于动量和动能,以下说法正确的是(   )

A:系统动量守恒的过程动能必定也守恒

B:系统动能守恒的过程动量必定也守恒

C:如果一个物体的动量保持不变,那么它的动能必然也保持不变

D:如果一个物体的动能保持不变,那么它的动量必然也保持不变

上一题 下一题 0.0难度 选择题 更新时间:2011-09-07 01:18:52

答案(点此获取答案解析)

C

同类题1

阅读理解。

     As the years go by, the Italian community has found its place in Australia. One of the main reasons is the birth of a second generation(代). The children of migrants(移民) have grown up as Australians.

    Lucy's family is an example.

    Lucy's parents came from Italy in the1950s. Lucy was born in Sydney soon after her parents arrived in Australia. Lucy's parents were both workers. They spoke Italian at home. When Lucy went to school she had to learn English. Her mum and dad could speak just a little English. Athome it was always Italian. When she got a bit older, her mum and dad would askher to help them out when they didn't understand something in English.

    When she was growing up, her parentsdidn't allow her to do as much as her Australian friends. Her friends didn't understand why she couldn't go out and do things with them, or why she alwaysdid what her parents wanted! Lucy's parents spent a lot of time with otherItalians, mainly because it was much easier for them to communicate in Italian. Because of this, she spent more time with kids from Italian background.

     Things have changed since Lucy had children of her own. Lucy is not as strict as her parents were, so her own kids have more freedom(自由). They can move between the different cultures and feel easier in both cultures. They haven't had so many problems about their identities(身份). They see themselves as Australians with an Italian background and they're proud of their traditions.