题干

如图所示,质量为m的小球从距离地面高H的A点由静止开始释放,落到地面上后又陷入泥潭中,由于受到阻力作用到达距地面深度为h的B点时速度减为零.不计空气阻力,重力加速度为 g.关于小球在刚接触地面到速度变为零的过程中,下列说法中正确的有(   )

A:小球的机械能减少了mgh

B:小球克服阻力做的功为mg(H+h)

C:小球所受阻力的冲量等于m 2gH

D:小球动量的改变量大小等于m 2gH

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B,D

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    Here are some English learning tips to help you improve your English.

    Ask yourself weekly: What do I want to learn this week?

    Asking yourself this question every week will help you think about what is most important to you. If you make a plan for each week, you will be surprised to notice how much you have improved your English by the end of the week! This feeling of success will encourage you to learn even more English.

Quickly review before going to bed

    Research has shown that our brains process(加工) information that is fresh in our brains while we sleep. By going over important knowledge before you go to sleep, your brain will work on this information while you sleep!

Speak English aloud.

    Understanding grammar rules does not mean you can speak English well. You need to practice speaking aloud. Speaking by yourself at home and reading the exercises that you are doing will help connect the muscles(肌肉)of your face to the information in your head and improve your pronunciation.

Do five to ten minutes of listening at least four times a week.

    If you decide that you are going to work hard and listen for two hours, maybe you will not do extra listening exercises soon. But if you listen five to ten minutes at least four times a week, you will find it's not so hard to develop the habit of listening to English.

Look for situations to practice your English.

    Learning English in a classroom is important, but using English in real situations will improve your English skills greatly. You can create new situations by using the Internet to listen to news, exchange emails in English with email friends, etc.

____on Learning English

Making a____ plan

※ In this way, you will be surprised to see the ____that you have made in your English by the end of the week.

※ You will be ____to learn even more English.

Reviewing before going to bed

※ Review before going to bed and you still process ____in your mind while sleeping.

Speaking as much as possible

※ Speaking English aloud can ____the muscles of your face with what you have learned and improve your____.

Listening more____

※ It will be ____ for you to develop the habit of listening to English if you listen often rather than once two hours a week.

Practicing English in

real situations

※ By ____ situations and using English, you will improve your English skills greatly.