题目内容

18. Owning a car in the countryside or a computer in this modern world may not be considered conspicuous consumption.

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19. New items, when first introduced, could be dismissed by some people who did not consider them useful.

20. A society’s way of life which requires physical work may depend in part on what and how much others consume.

1-12 一升降机以加速度l.22 m/s2上升，当上升速度为2.44 m/s时，有一螺丝自升降机的天花板上松脱，天花板与升降机的底面相距2.74 m. 计算：(l)螺丝从天花板落到底面所需要的时间；(2)螺丝相对升降机外固定柱子的下降距离．t=0.705 s; d=0.716 m

1-29 一无风的下雨天，一列火车以 v1 = 20.0 m/s的速度匀速前进，在车内的旅客看见玻璃窗外的雨滴和竖直线成75°下降．求雨滴下落的速度v2（设下降的雨滴作匀速运动．）v2 = 5.36 m/s