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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答案(点此获取答案解析)

B,D

同类题5

Every month, junior high schools in China choose one hero of the month. This person is a hero because he or she has done something to help protect animals in danger. Huang Jing decided to write a letter to the President of China.

Dear Mr. President,
I have been doing a project at school recently about animals in danger. I think the situation all over the world is really terrible. I am writing to you to suggest what China should do to help protect animals more.
I know that there are nearly 2,000 nature reserves in China, which is good. I live in Beijing and there are about 30 reserves outside the city. We visited one of them last month to see for ourselves.
I feel so sorry for the giant panda. It's one of the most popular animals in the world and a real symbol of China. We learned that pandas mainly live on bamboo, and that a panda can eat half its body weight of bamboo in 24 hours! That's a lot of bamboo. I think we should try to do more to stop cutting down forests. Pandas are already a rare animal and it would be so sad if they became extinct (灭绝) forever.
The other animal we should try to protect more is the Chinese alligator (扬子鳄). These creatures live in some parts of eastern China. These beautiful animals live in freshwater rivers and lakes but the water in some places isn’t clean enough for them to live in. It's really dirty in fact. The government should stop factories polluting the lakes and rivers.
If we protect these beautiful animals in China, more foreigners may wish to visit China to see them. They could be an important tourist attraction. It would be good if more people came to visit our beautiful country, especially to see the quieter areas in the country. Now most visitors just see the cities.
I hope you will encourage more people to think about such an important subject.
Sincerely yours,
Huang Jing