如图,物体由静止开始沿竖直放置的圆弧形光滑轨道下滑,在从A到C的下滑过程中,物体所受

题型:单项选择题

问题:

如图,物体由静止开始沿竖直放置的圆弧形光滑轨道下滑,在从A到C的下滑过程中,物体所受的合外力( )

A.大小不变,方向总是指向圆心

B.大小变化,方向总是指向圆心

C.大小不变,方向不总是指向圆心

D.大小变化,方向不总是指向圆心

考点:自学考试高等教育自学考试高等教育自学考试物理(工)真题2009年4月
题型:单项选择题

下列各句中,加点的成语使用恰当的一句是

A.我想靠迅速抓紧时间,去留住昙花一现的日子;我想凭时间的有效利用去弥补匆匆流逝的光阴。

B.年轻人的一个优点就是不会由于世俗的约束而畏蒽不前,而这种约束对于大多数成年人言通常似乎又很难摆脱。

C.贾宝玉的性格最突出的表现是,他不愿按贵族家庭为他安排好的道路亦步亦趋地生活,十分鄙弃功名富贵及其相关的世俗观念。

D.龙川岛像一张舒展着的荷叶漂浮在浩如烟海的千岛湖上,岛上又有30多个小湖,湖水明净,映着日光,犹如闪烁在荷叶上的水珠一样。

题型:单项选择题
阅读下面短文,从短文后各题所给的四个选项(A,B,C,D)中,选出可以填入空白处的最佳选项,并在答题卡上将该项涂黑。
For centuries, magicians have used various ways to shock the audience. We all have seen how a   36  performer carefully steps   37  a bed of burning coals -- barefoot. Then he walks across   38  a single burn on his feet. Is it mind over matter, or is it just physics? As it turns   __39 , walking on burning coals isn’t that hot as   40 . “The coals are hot enough to   41__  you, but if you walk quickly across them you   42  being burned.” says Jonathan Hall, a physician at Penn State University in Eric Pennsylvania.
That’s because some coals are made   43   burning wood chips. Wood has two   44__   properties(特性)for fire-walking, explains Hall. First, wood is an insulator(绝缘体)--it doesn’t   __45  heat very well. “It   46 _ time for heat to travel   47  the wood to your feet.” Hall says. If the performer walked across red-hot metal   48 , that would truly be   49 , because metal conducts, or transmits, heat very well. The metal would   50  burn a performer’s feet.
Second, wood has a low specific heat-- it doesn’t take much heat to   51  its temperature. Heat is a form of   52 . Temperature is a   53  of heat, in units of degrees. So   54  the coals are hot, the value(数值)of heat energy they contain is low. Thus, a well-trained performer can   55  such an amazing result.
Still, you don’t want to walk on burning coals, do you?
小题1:
A.daringB.dareC.roughD.fearful
小题2:
A.atB.overC.onD.above
小题3:
A.withB.withinC.withoutD.over
小题4:
A.out B.onC.offD.in
小题5:
A.imagineB.imaginedC.imaginingD.to imagine
小题6:
A.fireB.burnC.lightD.flame
小题7:
A.preventB.keepC.ignoreD.avoid
小题8:
A.offB.fromC.ofD.in
小题9:
A.idealB.classicC.favoriteD.standard
小题10:
A.transmitB.communicateC.bringD.send
小题11:
A.gathersB.takesC.gainsD.stands
小题12:
A.throughB.into C.overD.pass
小题13:
A.unhappyB.unharmedC.unhealthyD.unprepared
小题14:
A.charmingB.magicalC.trickyD.fashionable
小题15:
A.instantlyB.constantlyC.frequentlyD.lately
小题16:
A.produceB.raiseC.constructD.create
小题17:
A.powerB.sourceC.energyD.strength
小题18:
A.measureB.rankC.estimateD.rate
小题19:
A.what ifB.howeverC.as ifD.even though
小题20:
A.achieveB.arriveC.drawD.take
题型:单项选择题

简述第四代导演的艺术特征。

题型:单项选择题

关于探测器的特性,不包括()

A.转换效率

B.响应时间

C.散热率

D.稳定性

E.动态范围

题型:单项选择题

PM2.5是造成重庆市冬春季节大气污染的重要原因,那么重庆市PM2.5的主要来源是哪一些?()

A.交通污染

B.扬尘污染

C.工业污染

D.生活污染

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