问题 填空题

三个共点力的大小分别为2N、8N、9N,则它们的合力的最大值为______N;合力的最小值为______N.

答案

当三个力同向时,合力最大,为19N;由于任意一个力在另外两个力的合力之差与合力之和之间,所以三力可以平衡,即三个力合力能够为零,则合力最小值为0.

故答案为:19,0.

阅读理解

阅读短文,完成下列小题。

                                                                                                                          Mr. and Mrs. J Halstead 

                                                                                                                          5b Ashton Drive

                                                                                                                          Portsmouth 

                                                                                                                          Po57BU

                                                                                                                          Reino Unido

Dear Mum and Dad,

     Well, here I am in Peru on our South American tour. We got to Lima five days ago. We had a good

journey. It took three days by bus, but we saw lots of things on the way. We didn't do much for the first

two days, as a couple of other guys were ill. We spent most of the time on the beach. (They're OK now!)

On Wednesday we came up to the mountains, and yesterday we went to the old Inca city of Machu

Picchu and did some sightseeing. It was wonderful! We didn't have a lot of time there, but we saw

everything and I took lots of photos. And we're off to Bolivia tomorrow!

      Hope you're well. Did you get my card from Colombia? 

                                                                                                                                                   Love

                                                                                                                                                   Matt

1. Mr. Halstead is Matt's ________.

2. Matt got to ________ five days ago.

3. Matt didn't do much for the first two days because ________.

4. Where did Matt spend three days?

    _________________________________________________.

5. Wherewill they go tomorrow?

    _________________________________________________.

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