问题 计算题

如图所示,把质量m1=4 kg的木块叠放在质量m2=5 kg的木块上。m2放在光滑的水平面上,恰好使m1相对m2开始滑动时作用于木块m1上的水平拉力F1=12 N。那么,至少应用多大的水平拉力F2拉木块m2,才能恰好使m1相对m2开始滑动?

答案

15 N

阅读理解

In England, people often talk about the weather because they can experience (经历) four seasons in one day. In the morning the weather is warm just like in spring. An hour later black clouds come and then it rains hard. The weather gets a little cold. In the late afternoon the sky will be sunny, the sun will begin to shine, and it will be summer at this time of a day.

In England, people can also have summer in winter, or have winter in summer. So in winter they can swim sometimes, and in summer sometimes they should take warm clothes.

When you go to England, you will see that some English people usually take an umbrella (伞)or a raincoat with them in the sunny morning, but you should not laugh at them.

If you don't take an umbrella or a raincoat, you will regret (后悔) later in the day.

小题1:Why do people in England often talk about the weather?

A.Because they may have four seasons in one day

B.Because they often have very good weather

C.Because the weather is warm just like in spring

D.Because the sky is sunny all day小题2:From the story we know that when _________come, there is a heavy rain.

A.sunshine and snow

B.black clouds

C.summer and winter

D.spring and autumn小题3:"People can also have summer in winter." Means "it is sometimes too ______in winter."

A.warm

B.cool

C.cold

D.rainy小题4:In the sunny morning some English people usually take a raincoat or an umbrella with them because ________.

A.their friends ask them to do so

B.it often rains in England

C.they are going to sell them

D.they are their favourite things小题5:The best title (标题)for this passage is ________.

A.Bad Seasons

B.Summer or Winter

C.The Weather in England

D.Strange English People

多项选择题