问题 选择题

皮带传送机的皮带与水平方向的夹角为,如图所示,将质量为m的小物块放在皮带传送机上,随皮带一起向下以加速度a做匀加速直线运动,则(   )

A.小物块受到的支持力的方向一定垂直于皮带指向物块

B.小物块受到的静摩擦力的方向一定沿皮带斜向下

C.小物块受到的静摩擦力的大小可能等于

D.小物块受到的重力和摩擦力的合力的方向一定沿斜面方向

答案

AC

小物体受重力、支持力和静摩擦力作用,受力如图,

根据牛顿第二定律得,mgsinα+f=ma,解得f=ma-mgsinα>0,所以小物体所受静摩擦力大小为ma-mgsinα,方向沿皮带向下.支持力的大小为mgcosα,当=mg时,支持力和静摩擦力的合力等于mg.

ma-mgsinα可能等于mgsinα,但是重力的方向竖直向下,静摩擦力的方向沿斜面向下,则重力和静摩擦力合力的方向一定不沿传送带.

阅读理解

It’s only 4 hours flying time from Sydney, but a world away. What better place to rest than a country where the only place people hurry is on the football field and things are done in “Fiji time”?

Viti Levu – Great Fiji – is the largest island. Here you’ll find the capital Suva and the international airport at Nadi. Vatoa, on the other hand, is a tiny island in the farthest part of Fiji. Then there are 331 other islands, many of them with places to stay.

Whit less than a million people living on islands, you’ll never feel crowded. And with a climate(气候) that changes only for five degrees between seasons, there’s never a bad time to come.

From cities to villages, from mountains to beaches, from water sports to wooden artworks, Fiji can give you more adventures and special experiences than you could find almost anywhere in the world.

Whenever you come, wherever you go, you’re sure to see some unforgettable events. From war dances to religious(宗教的) songs. From market days to religious days. It’s not just staged for tourists; it’s still a part of everyday life in Fiji. And any one of us can enjoy Fiji’s spirit by being part of the traditional(传统的) sharing of yaqona, a drink made from the root of a Fiji plant.

So why not join us for the experience of a life me?

小题1:Where is the international airport of Fiji?

A.In Suva.

B.In Sydney.

C.On the island of Vatoa.

D.On the island of Viti Levu.小题2:What does the text tell us about Fijian people?

A.They invented “Fiji time” for visitors.

B.They stick to a traditional way of life.

C.They like to travel from place to place.

D.They love taking adventures abroad.小题3:One of the things that make Fiji a tourist attraction is _______.

A.it’s comfortable hotels

B.its good weather all year round

C.its exciting football matches

D.its religious beliefs小题4:Where can we most probably read this text?

A.In a personal diary

B.In a science report

C.In a travel magazine

D.In a geography textbook

单项选择题