问题 计算题

如图所示,竖直放置的U形导轨宽为L,上端串有电阻R(其余导体部分的电阻都忽略不计),磁感应强度为B的匀强磁场方向垂直于纸面向外。金属棒ab的质量为m,与导轨接触良好,不计摩擦.从静止释放后ab保持水平而下滑。说明导体棒的运动性质,试求最大加速度a和导体棒下滑的最大速度vm.

答案

说明运动性质释放瞬间ab只受重力,开始向下加速运动。随着速度的增大,感应电动势E、感应电流I、安培力F都随之增大,加速度随之减小.当F增大到F=mg时,加速度变为零,这时ab达到最大速度. 以后匀速直线运动                              ……(6分)

由上面分析得初始加速度最大   am="g         " ……(2分)

由上面分析得初始速度最大时,可得           ……(4分)

阅读理解

Just five one-hundredths of an inch thick, light golden in colour and with a perfect “saddle curl”( 马鞍状卷曲 ), the Lay’s potato chip seems an unlikely weapon for global domination. But its maker, Frito-Lay, thinks otherwise. “Potato chips are a snack food for the world,” said Salman Amin, the company’s head of global marketing. Amin believes there is no corner of the world that can resist the charms of a Frito-Lay potato chip.

Frito-Lay is the biggest snack maker in America owned by PepsiCo, and accounts for over half of the parent company’s $3 billion annual profits. But the U.S. snack food market is largely saturated( 市场基本饱和 ), and to grow, the company has to look overseas.

Its strategy rests on two beliefs: First, a global product offers economies of scale with which local brands cannot compete. And second, consumers in the 21st century are drawn to “global” as a concept. “Global” does not mean products that are consciously identified as American, but ones that consumers--- especially young people--- see as part of a modern, innovative( 创新的 ) world in which people are linked across cultures by shared beliefs and tastes. Potato chips are an American invention, but most Chinese, for instance, do not know that Frito-Lay is an American company. Instead, Riskey, the company’s research and development head, would hope they associate the brand with the new world of global communications and business.

With brand perception a crucial factor, Riskey ordered a redesign of the Frito-Lay logo. The logo, along with the company’s long-held marketing image of the “irresistibility” of its chips, would help facilitate the company’s global expansion.

The executives ( 行政主管 )acknowledge that they try to swing national eating habits to a food created in America, but they deny that amounts to economic imperialism(帝国主义). Rather, they see Frito-Lay as spreading the benefits of free enterprise across the world. “We are making products in those countries, we’re adapting them to the taste of those countries, building businesses and employing people and changing lives,” said Steve Reinemund, PepsiCo’s chief executive. 

72. It is the belief of Frito-Lay’s head of global marketing that _____.

A. People over the world enjoy eating their company’s potato chips

B. Their company must find new ways to promote domestic sales

C. The light golden color enhances the charm of their company’s potato chips

D. Potato chips can hardly be used as a weapon to dominate the world market

73. One of the assumptions on which Frito-Lay bases its development strategy is that _______.

A. products identified as American will have promising market value

B. local brands cannot compete successfully with American brands

C. products suiting Chinese consumers’ needs bring more profits

D. consumers worldwide today are attracted by global brands

74. Why did Riskey have the Frito-Lay logo redesigned? ______

A. To suit changing tastes of young consumers.

B. To change the company’s long-held marketing image.

C. To promote the company’s strategy of globalization.

D. To compete with other American chip producers.

75. Frito-Lay’s executives claim that the promoting of American food in the international market ______.

A. won’t affect the eating habits of the local people

B. will be in the interest of the local people

C. will lead to economic imperialism

D. won’t spoil the taste of their chips 

单项选择题