问题 多选题

做变速直线运动的物体,在t时间内位移为s,它在位移中点

s
2
的速度为v1,在中间时刻
t
2
的速度为v2.则以下说法正确的是(  )

A.当物体做匀加速直线运动时,v1>v2

B.当物体做匀减速直线运动时,v1>v2

C.当物体做匀加速直线运动时,v1<v2

D.当物体做匀减速直线运动时,v1<v2

答案

如图作出v-t图象,由图可知中间时刻的速度v2,因图象与时间图围成的面积表示物体通过的位移,故由图可知

t
2
时刻物体的位移小于总位移的一半,故中间位置应在中间时刻的右侧,故此时对应的速度一定大于v2

故A正确;同理可知,若物体做匀减速直线运动,结果相同,故B正确

故选AB.

阅读理解

Dublin has the benefit of being a home to unequaled beaches.They can be especially attractive during the summer season.Experience this scenery for yourself and see what these beaches have to offer you.

Finding yourself at Dollymont makes you a fortunate tourist especially if you find beaches irresistible. Here you can swim away your worries through the Dollymont Blue Flag Beach.The beach provides a wonderful view which is perfect for some relaxing moments.Its shoreline is well recommended for a few quiet and unworried walks along the beach.

For some beach adventure, you can drive your way down the M50 and M 1 motorways to Donabate. This village in North County Dublin offers an attractive Blue Flag beach which is perfect for your swimming addictions.Lifeguards are on call during bathing period.The water is as overpowering as the surrounding.

For a double purpose beach, check out Killiney.This beach is a top off destination for a swimming adventure and it is equally grand for relaxing walks. The shoreline is covered with pebbles and rocks.This may seem averred with ordinary stony beach for some but for those who have strong interest in geological processes, Killiney is a best spot to discover part of.Dublin's history and Killiney's formation.

Another accessible Blue Flag Beach lies on Malahide in Fingal.You can enjoy the distinctive attraction of the water while still getting yourself amazed with the wonderful sights around Malahide.Beach is sandy and holds a harbor designed for pleasure boats at the Northern end.

For a bit of challenge and thrill, consider a swim at Seapoint Beach in Dun Laoghaire Rathdown.You can have the pleasure of an exciting surf adventure here apart from the usual swimming activity.This is often visited by tourists due to its various appeals: swimming on the north part of the beach while surfing, boating and jet skiing at the south.

Need to beat the heat off your summer vacation? There is nothing as satisfying as a visit to some of these outstanding beaches.

小题1:How many beaches are mentioned in this article?

A.Five

B.Four

C.Three

D.Two小题2:If you are visiting Killiney, which of the following activities can't you do?

A.Having a swimming adventure.

B.Having some relaxing walks.

C.Discovering some Dublin's history.

D.Practising operating boats for pleasure.小题3:Some tourists choose a swim at Seapoint Beach probably because they can _____.

A.get themselves interested in the sights around

B.have a wonderful surf on the north of the beach

C.enjoy several unusual and exciting activities

D.call the lifeguards during bathing period小题4:If you want to be quiet and have same relaxing walks, you may pay a visit to _____.

A.Dollymont and Donabate

B.Donabate and Malahide

C.Dollymont and Killiney

D.Killinev and Malahide小题5:The best title of this article should be _____.

A.Where to go swimming in summer

B.Beating off the heat in Dublin

C.Benifits of staying at beaches

D.Geological researches in vacation

单项选择题

人类正面临着全球变暖的挑战。联合国的一份报告向我们描述了气候变化将产生的灾难性后果;森林消失和沙漠扩大,将使非洲成为受影响最广的地区;热带流行的疟疾和寄生虫病将向北蔓延,使欧洲出现流行病;地中海地区由于严重缺水将会半沙漠化,滑雪运动在欧洲将会荡然无存;在英国,肆虐的冬季风暴将变得司空见惯,东部的某些地方可能因变得过于干旱而无法种植各类作物。另外,一些河流水量将大大减少甚至干涸,饮用水源遭到破坏,昔日绕道而行的台风将频频袭击日本,致使短时间内大量降水,洪水泛滥,城市淹没,山体滑坡,交通中断;而最为严重的影响是地球上数以百万计的人将由于海岸线受侵蚀、海岸被淹没和农业生产遭破坏而被迫离开家园。 最新的一项研究表明,到21世纪末,地球平均气温将比现在升高3℃。这一预测是以近年来地球气温升高的现象和温室效应为依据的。温室效应,在物理学上是指透射阳光的密闭空间由于与外界缺乏对流等热交换而产生的保温效应。大气层中的二氧化碳在大气层中的含量直接影响着地表热量向空间的散失,使大气层保持一定的热能。二氧化碳在大气层中的含量直接影响着地表气温,当大气层中的二氧化碳增加时,地表气温就相应升高。科学家认为,大气中的二氧化碳在地球环境的演化中起着极其重要的作用,如果没有大气层的保温作用,全球气温将为-4℃,而现在的全球平均气温为16℃。科学家们预言,人类如不采取果断和必要的措施,到2030年,大气中二氧化碳的含量将比1850年工业革命时增加一倍。 导致大气层中二氧化碳含量上升的原因是显而易见的。工业革命开始以后,化石燃料(煤炭、石油、天然气)的燃烧量越来越大,使大气中二氧化碳的浓度不断增加。同时,雷击、虫害、砍伐造成的森林火灾、草地衰退和森林破坏也使能够吸收二氧化碳的绿色植物遭到破坏。所以,要控制全球变暖,必须改变能源结构,大力植树造林。有科学家指出,只有以核燃料代替化石燃料,才能从根本上防止温室效应的加剧。 气候是人类赖以生存的条件,全球气候变暖是人类自身活动所造成的灾难。我们必须树立全球共同性的大气环境观念,为自身的生存和发展,爱护头顶上的这片蓝天。

根据原文,全球气温变暖带来的影响最严重的一项是()。

A.河流水量减少甚至干涸,饮用水源遭到破坏,导致不少地区沙漠扩大,疾病流行

B.肆虐的冬季风暴将变得司空见惯,一些地区会因为过于干旱而无法种植各类作物

C.数以百万计的人因海岸线受侵蚀、海岸被淹没和农业生产遭破坏而被迫离开家园

D.台风频频袭击,致使短时间内大量降水,洪水泛滥,城市淹没,山体滑坡,交通中断