问题 问答题

如图所示,MN是竖直放置的长L=0.5m的平面镜,观察者在A处观察,有一小球从某处自由下落,小球下落的轨迹与平面镜相距d=0.25m,观察者的眼睛到镜面的距离s=0.5m,小球从静止开始下落0.275s后,观察者才能在镜中看到小球的像,求观察者在镜中看到小球像的时间△t为多少?(取g=10m/s2

答案

根据平面镜作图方法做出光路图如图所示,小球在下落过程中从B到C过程人眼睛才能看到,由几何知识应有

MN
BC
=
s
s+d
=
2
3
,所以BC=
3
2
MN
=
3L
2
=0.75m,

再由自由落体规律可得:OB=

1
2
gt
=
1
2
×10
×0.275
m=0.378m,所以OC=OB+BC=1.128m

设观察者能在镜中看到小球像的时间为△t,则OC=

1
2
g(t+△t
)
=
1
2
×10×(0.275+△t
)
,代入数据解得△t=0.2s

故观察者在镜中看到小球像的时间△t为0.2s.

解答题
单项选择题

Passage One

Most students arrive at college using" discrete, concrete and absolute categories to understand people, knowledge, and values. " These students live with a dualistic view, seeing "the world in polar terms of we-right-good vs. other-wrong-bad. " These students cannot acknowledge the existence of more than one point of view toward any issue. There is one "right" way. And because these absolutes are assumed by or imposed on the individual from external authority, they cannot be personally substantiated or authenticated by experience. These students are slaves to the generalizations of their authorities. An eye for an eye! Capital punishment is apt justice for murder. The Bible says so.

Most students break through the dualistic stage to another equally frustrating stage—multiplicity. Within this stage, students see a variety of ways to deal with any given topic or problem. However, while these students accept multiple points of view, they are unable to evaluate or justify them. To have an opinion is everyone’s right. While students in the dualistic stage are unable to produce evidence to support what they consider to be self-evident absolutes, students in the multiplistic stage are unable to connect instances into coherent generalizations. Every assertion, every point, is valid. In their democracy they are directionless. Capital punishment What sense is there in answering one murder with another

The third stage of development finds students living in a world of relativism. Knowledge is relative: right and wrong depend on the context. No longer recognizing the validity of each individual idea or action, relativists examine everything to find its place in an overall framework. While the multiplist views the world as unconnected, almost random, the relativist seeks always to place phenomena into coherent larger patterns. Students in this stage view the world analytically. They appreciate authority for its expertise, using it to defend their own generalizations. In addition, they accept or reject ostensible authority after systematically evaluating its validity. In this stage, however, students resist decision making. Suffering the ambivalence of finding several consistent and acceptable alternatives, they are almost overwhelmed by diversity and need means for managing it. Capital punishment is appropriate justice—in some instances.

In the final stage students manage diversity through individual commitment. Students do not deny relativism. Rather they assert an identity by forming commitments and assuming responsibility for them. They gather personal experience into a coherent framework, abstract principles to guide their actions, and use these principles to discipline and govern their thoughts and actions. The individual has chosen to join a particular community and agrees to live by its tenets. The accused has had the benefit of due process to guard his civil rights, a jury of peers has found him guilty, and the state has the right to end his life. This is a principle my community and I endorse.

Which one of the following best describes the organization of the passage ?()

A.Four methods of thought are compared and contrasted.

B.It is shown how each of four types of thought evolved from each other.

C.Four methods of thought are presented, and each is shown to complement the other.

D.The evolution of thought through four stages is presented, and each stage is illustrated by how it views capital punishment.