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问题 计算题

【选修3-5选做题】

如图所示，在水平光滑直导轨上，静止着三个质量均为m=1 kg的相同小球A、B、C，现让A球以v0=2 m/s的速度向B球运动，A、B两球碰撞后粘合在一起，两球继续向右运动并跟C球碰撞，碰后C球的速度vC=1 m/s。求：

（1）A、B两球碰撞后瞬间的共同速度；

（2）两次碰撞过程中损失的总动能。

答案

解：（1）A、B相碰满足动量守恒mv0=2mv1

得A、B两球碰撞后瞬间的共同速度v1=1 m/s

（2）两球与C碰撞同样满足动量守恒2mv1=mvc+2mv2

两次碰撞损失的动能

选择题

香港人多地狭，扩展城市建设用地往往采用“上天”、“下海”的方式，对这两种方式的正确理解是①建设高层建筑②居住在船上③向月球移民④填海造陆[ ]

A．①和③

B．③和④

C．②和④

D．①和④
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填空题

Some consumer researchers distinguish (1) "rational" motives and "emotional" (or "non-rational") motives. They use the term "rationality" (2) the traditional economic sense that assumes (3) consumers behave rationally when they carefully consider all alternatives (4) choose those that give them the greatest utility (i.e., satisfaction). (5) a marketing context, the term "rationality" implies that the consumer selects goods based (6) totally objective criteria, such (7) size, weight, price, and so on. "Emotional" motives imply the selection of goods (8) to personal or subjective criteria—the desire (9) individuality, pride, fear, affection or status.
The assumption underlying this distinction is (10) subjective or emotional criteria do not maximize utility or satisfaction. (11) , it is reasonable to assume that consumers always attempt to select alternatives that, (12) their view, serve to maximize satisfaction. Obviously, the assessment of satisfaction is a very personal process, based (13) the individual’s own needs as (14) as on past behavioral, social, and learning experiences. What may appear (15) irrational to an outside observer may be perfectly rational (16) the context of the consumer’s own psychological field. For example, a product purchased to enhance one’s self-image (such as a fragrance) is a perfectly rational form of consumer behavior. (17) behavior did not appear rational to the person who undertakes it (18) the time that it is undertaken, obviously he or she would not do it. (19) the distinction between rational and emotional motives does not appear to be warranted.
Some researchers go so far (20) to suggest that emphasis (21) "needs" obscures the rational, or conscious, nature of most consumer motivation. They claim that consumers act consciously (22) maximize their gains and minimize their losses; that they act not (23) subconscious drives but from rational preferences, (24) what they perceive to be (25) their own best interests.
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