题干

如图所示,轻绳一端系在质量为m的物块A上,另一端系在一个套在粗糙竖直杆MN的圆环上.现用水平力F拉住绳子上一点O,使物块A从图中实线位置缓慢下降到虚线位置,但圆环仍保持在原来位置不动.在这一过程中,环对杆的摩擦力F1和环对杆的压力F2的变化情况是(  )

A:F1保持不变,F2逐渐增大

B:F1保持不变,F2逐渐减小

C:F1逐渐增大,F2保持不变k*s5u

D:F1逐渐减小,F2保持不变

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B

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    The U.S. Postal Service(USPS) is losing billions of dollars a year. The government company that delivers "small mail" is losing out to email and othertypes of electronic communication. First-classmail amount fell from a high point of 104 million pieces in 2000 to just 64million pieces by 2014.

    Congress permits the 600,000-empIoyee USPS to hold a monopoly (垄断) overfirst-class and standard mail. The company pays no federal, state or local taxes; pays no vehicle fees; and is free from many regulations on other businesses. Despite these advantages, the USPS has lost $52 billion since 2007, and will continue losing money without major reforms.

    The problem is that Congress is preventing the USPS from reducing costs as its sales decline, and is blocking efforts to end Saturday service and close unneeded post office locations. USPS also hasa costly union-dominated work force that slows the introduction of new ideas ormethods down. USPS workers earn significantly higher payment than comparable private-sector workers. The answer isto privatize the USPS and open postal markets to competition. With the riseof the Internet, the argument that mail is a natural monopoly that needs government protection is weaker than ever.

    Other countries facing declining letter amounts have madereforms. Germany and the Netherlands privatized their national postal companies over a decade ago, and other European countries have followed suit. Britain floated shares of the Royal Mail on its stock exchange in 2013. Some countries, such us Sweden and New Zealand, have not privatized their national postal companies, but they have opened them up to competition.

    These reforms have driven efficiency improvements in all of these countries. Additional number of workers have been reduced, productivity has risen and consumers have benefited. Also, note that cost-cutting measures—such as closing tone post offices—are good for both the economy and the environment.

    Privatization and competition also encourage new changes. When the USPS monopoly over "extremely urgent" mail was stopped in 1979, we saw an explosion in efficient overnight private delivery by firms such as FedEx.

    The government needs to wake up to changing technology, study postal reforms abroad and let businessmen reinvent our out-of-date postal system.

同类题5

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