题干

在“探究功与速度变化的关系”实验中,小车在运动中会受到阻力作用.这样,在小车沿木板滑行的过程中,除橡皮筋对其做功以外,还有阻力做功,这样便会给实验带来误差,我们在实验中想到的办法是使木板略微倾斜,对于木板的倾斜程度,下面说法中正确的是(  )

A:木板只要稍微倾斜一下即可,没有什么严格的要求

B:木板的倾斜角度在理论上应满足下面条件:即重力使物体沿斜面下滑的分力应等于小车受到的阻力

C:如果小车在木板上差不多能做匀速运动,就说明木板的倾斜程度是符合要求的

D:其实木板不倾斜,问题也不大,因为实验总是存在误差的

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B

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School BBS   About life in England

A: Many English people live in houses, not in apartments. Most houses have gardens. Many young people don't live with their parents.

B: School starts at about nine o'clock in the morning and finishes at about three o'clock in the afternoon. All the children go to school when they are four or five years old.

C: Most office workers start to work at about nine in the morning, and finish work at about five or six in the afternoon. Most people don't go home for lunch, and they just have a quick meal!

D: Most shops open at about nine o'clock in the morning and close at about eight o'clock in the evening. People can buy fast food or life things in the shops.

E: In the evenings, I usually do my homework before watching TV. Mum helps me with my homework. My family like to watch Coronation Street (an English soap opera).

F: The second most popular activity in England is visiting friends or relatives. Mum and Dad go out and visit friends at least once a week.

①They usually go to work by bus, and they work with computers. ____

②I have to help Mum wash the dishes after meals. I also have to clean my bedroom. ____

③On weekends, many families go to the open market. People sell vegetables, clothes, toys, and anything else out on the street. ____

④Most families have a car, a computer, a washing machine, etc. Almost everyone has a mobile phone. ____

⑤Most children take a lunch box to school. There are usually things like sandwiches, fruit and a bag of French fries in it. ____