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一光滑圆环固定在竖直平面内,环上套着两个小球A和B(中央有孔),A、B间由细绳连接,它们处于如图所示位置时恰好都能保持静止状态.此情况下,B球与环中心O处于同一水平面上,AB间的细绳呈伸直状态,与水平线成30°夹角.已知B球的质量为1kg,取g=10m/s2,求:

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    A recent study by Citi Retail Services found that a growing number of people are embracing digital wallets or e-wallets, due in large part to their convenience and ease of use.

    E-wallets have been called the future of real-world payment technology.With major players like Alipay,WeChat and Apple Pay becoming popular,it seems to be a safe bet that a change in consumer payment technology is coming soon.

    CNN reporter Paul Ripley experienced a day in Beijing without his wallet."In China's largest cities, you can definitely survive without carrying a pocket full of cash and credit cards-as long as you've got your smartphone."He paid for breakfast by scanning a QR code on the window of a hole-in-the-wall restaurant.All he had to do was to enter a password and the transaction was complete.

    Unlike the situations in the US and other countries,"China doesn't have a really money-making credit card system, so Chinese people just skipped credit cards and went straight to mobile payments."Gu Yu,co-founder of the new payment app Mileslife,told CNN.He also pointed out the advantages of mobile payments."No coins or bills that can be lost or stolen. electronic receipts, the ease of keeping rack of spending-and of course,no wallet taking up space."he said.

    However, if we want to make e-wallets a mainstream trend a lot of things will have to change over the coming years.Perhaps one of the most important things that need to be changed is how people regard e-wallets.Linda Barrabee,research director for NPD Connected Intelligence, said in a statement."In order to promote on-the-go consumer transactions and commerce, wireless carriers, credit card companies, and e-commerce companies need to make sure the process is convenient,simple,and secure for consumers."