题目

火车沿平直轨道以20 m/s的速度向前运动，司机发现正前方50 m处有一列火车正以8 m/s的速度沿同一方向行驶，为避免相撞，司机立即刹车，刹车的加速度大小至少应是A.1 m/s2 B.2 m/s2 C.0.5 m/s2 D.1.44 m/s2 答案：【答案】D【解析】设经时间t客车速度与货车相等，轿车刹车的加速度大小为a，则：由，解得此时，轿车的位移为s0，有：货车的位移为s1，有：得a==1.44 m/s2故D正确，ABC错误。故选DThe question of whether war is inevitable is one which has concerned many of the world’s great writers. Before1 this question, it will be useful to introduce some2concepts. Conflict,3 as opposition among social units-or individuals-directed against one another, is4from competition, which5 opposition among social units6seeking to obtain something which is7 inadequate supply. Competitors may not know about one another, which those who8in a conflict do. Conflict and competition are both9 of opposition. The meaning of opposition has been stated as a process by which social unit function in the disservice of one another, opposition is10contrasted to cooperation, a11 by which social units function in the service of one another. These12are necessary because it is important to emphasize that competition between individuals or groups is inevitable in a world of limited13 , but conflict isn’t . Conflict, nevertheless, is very likely to occur and is probably an essential and desirable14of human societies. Many authors have15 their arguments that war cannot be avoided on the idea that in the struggle for existence among groups of animals, only those which are best16remain alive. In general, however, this struggle in nature is competition, not conflict. Those who fail in this competition17 starve to death or are18 by other types of animals. This struggle for19is not similar to human war, but is like the competition of20 for jobs, markets, and materials. The most important quality of this struggle is the competition for the necessities of life that are not enough to satisfy all.1.A.consideringB.solvingC.answeringD.saying2.A.relatedB.usedC.translatedD.sacred3.A.specifiedB.remarkedC.definedD.claimed4.A.variableB.distinguishedC.variousD.isolated5.A.acknowledgedB.deniesC.assumesD.means6.A.criticallyB.approximatelyC.independentlyD.costly7.A.onB.forC.withD.in8.A.enterB.participateC.fallD.involve9.A.formationsB.classesC.termsD.reactions10.A.neverthelessB.howeverC.thusD.maybe11.A.processionB.standardC.processD.measurement12.A.accountsB.definitionsC.descriptionsD.explanations13.A.resourcesB.originsC.sourcesD.materials14.A.matterB.elementC.eventD.coincidence15.A.concentratedB.fixedC.centeredD.based16.A.encouragedB.acceptedC.adaptedD.adopted17.A.not onlyB.eitherC.neitherD.both18.A.killedB.raisedC.firedD.surrounded19.A.resistenceB.privilegeC.favourD.employment20.A.workersB.officialsC.individualsD.residents