题干

下列说法正确的是(   )

A:可把动量定理表述为:物体动量的变化率等于它受的合外力

B:力与力的作用时间的乘积叫做力的冲量,它反映了力的作用对时间的累积效应,是一个标量

C:动量定理的物理实质与牛顿第二定律是相同的,但有时用起来更方便

D:易碎品运输时要用柔软材料包装,船舷常常悬挂旧轮胎,都是为了延长作用时间以减小作用力

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答案(点此获取答案解析)

A,C,D

同类题2

阅读下面材料,从每题所给的A、B、C、D四个选项中选出最佳选项。

B

    Language students often think they have memory problems. They worry because they can't remember words. In fact, the problem usually isn't with their memory. The problem is with how they study.

    To remember words better, you need to understand how memory works. There are two kinds of memory: short-term and long-term. When you see, hear, or read something, it goes first into short-term memory. But short-term memory lasts for only a few seconds. You will only remember something longer if it goes into long-term memory. Your long-term memory is like a very big library with many, many books. And like a library, it's organized (有条理的). When you put away a book – or memory – you can't just leave it anywhere. You have to choose a place where you can find it again.

    How can you do this with vocabulary? The answer is to work with the word and think about the word in new ways. You can do this by writing new sentences that include it. Even better, you can invent a little story about the word, with people or places that you know. Another way is to make a picture in your mind with the word. For example, if the word is height, you can think of the tallest person you know and try to guess his or her height. All of these activities are good ways to think about words. They make the meaning of words stronger in your long-term memory. And they give a way to find a word when you need it.