问题 问答题

如图所示,有一个楔形槽ABC,槽底边AC水平,一钢球置于槽内,现给钢球施加一个水平方向的推力F。

(1)分析槽壁对钢球的弹力;

(2)若将F去掉,再分析槽壁对钢球的弹力。

答案

(1)钢球在水平推力作用下,与AB壁和AC壁相互挤压,因而钢球与AB壁、AC壁间均有弹力产生。AB对钢球的弹力垂直AB向下,AC对钢球的弹力竖直向上;

(2)去掉水平外力后,钢球只与AC壁挤压,受到AC对钢球竖直 向上的弹力。而AB与钢球虽接触但并未产生形变,因为此时把AB去掉,钢球仍可静止于AC壁上。

单项选择题

Cooperation is the common endeavor of two or more people to perform a task or reach a jointly cherished goal. Like competition and conflict, there are different forms of cooperation, based on group organization and attitudes.In the first form, known as primary cooperation, group and individual unite. The group contains nearly all of each individual’’s life. The rewards of the group’’s work are shared with each member. There is an interlocking identity of individual, group, and task performed. Means and goals become one, for cooperation itself is valued.While primary cooperation is most often characteristic of preliterate societies, secondary cooperation is characteristic of many modern societies. In secondary cooperation, individuals devote only part of their lives to the group. Cooperation itself is not a value. Most members of the group feel loyalty, but the welfare of the group is not the first consideration. Members perform tasks so that they can separately enjoy the fruits of their cooperation in the form of salary, prestige, or power. Business offices and professional athletic teams are examples of secondary cooperation.In the third type, called tertiary cooperation or accommodation, latent conflict underlies the shared work. The attitudes of the cooperating parties are purely opportunistic; the organization is loose and fragile. Accommodation involves common means to achieve antagonistic goals; it breaks down when the common means cease to aid each party in reaching its goals. This is not, strictly speaking, cooperation at all, and hence the somewhat contradictory term antagonistic cooperation is sometimes used for this relationship.

Which of the following statements about primary cooperation is supported by information in the passage

A.It was limited in prehistoric times.

B.It is usually the first stage of cooperation achieved by a group of individuals attempting to cooperate.

C.It is an ideal that can never be achieved.

D.It is most commonly seen among people who have not yet developed reading and writing skills.

单项选择题