题干

小磊同学是班里的“大力士”,一天他放学回家,看到公路上有一块大石头,他担心大石头会妨碍车辆正常通行.于是,他决定把石头推到路边,但是他费了很大的力,累得满头大汗,石头却一点儿没动(如图所示).他的同学小颖恰好路过,看到此清景说:“你的行为很值得称赞,但是你对石头并没有做功.”你认为小磊同学对石头做功了吗?为什么?

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答案(点此获取答案解析)

解:小磊对石头没有做功.根据做功的两个必要因素:一是有力作用在物体上,二是物体在力的方向上通过了距离.小磊对石头虽然用了力,但石头没有在力的方向上通过距离.因此,小磊没有对石头做功

同类题3

根据短文内容,从短文后的七个选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

    Many parents would like to teach their children English at home, but don't know how to start. It doesn't matter if your own English is not perfect. The most important thing is that you give your children lots of encouragement and praise.____ They will need some time to learn the language.

Make it a rule

    Try to do certain activities at the same time every day.____ For example, you could read an English story with your children before bedtime. Repetition (重复) is important — children often need to hear words many times before they say them themselves.

Playing games

    ____ Cards are a great way to teach words and there are many different games which you can play with cards, such as Memory and Happy Families.

Using everyday situations

    The advantage of teaching English at home is that you can use everyday situations to practice the language naturally. For example:

    Talk about clothes when your child is getting dressed ("Let's put on your blue socks", etc.).

    ____When you go to the supermarket, give your child a list of things to find.

    Using songs

    Songs are a really good way to learn new words. Songs with actions are especially good for very young children because they are able to join in.____

A. Fifteen minutes is enough for very young children.

B. Children learn naturally when they are having fun.

C. Teach food words when you are cooking or going shopping.

D. The actions often show the meaning of the words in the song.

E. With younger children, there is no need to teach grammar rules.

F. Don't worry if your child doesn't start speaking English immediately.

G. Children feel more comfortable and confident when they know what to expect.