问题 计算题

如图所示,两个可导热的气缸竖直放置,它们的底部由一细管连通(忽略细管的容积)。两气缸各有一活塞,质量分别为,活塞与气缸壁无摩擦。活塞的下方为理想气体,上方为真空。当气体处于平衡状态时,两活塞位于同一高度h。(已知=3m,=2m)

(1)在两活塞上同时各放一质量为m的物块,求气体再次达到平衡后两活塞的高度差(假定环境的温度始终保持为)。

(2)在达到上一问的终态后,环境温度由缓慢上升到T,试问在这个过程中,气体对活塞做了多少功?气体是吸收还是放出了热量?(假定在气体状态变化过程中,两物块均不会碰到气缸顶部)

答案

⑴两活塞的高度差为

在此过程中气体吸收热量

⑴设左、右活塞的面积分别为A/和A,由于气体处于平衡状态,故两活塞对气体的压强相等,即:  

由此得:  

在两个活塞上各加一质量为m的物块后,右活塞降至气缸底部,所有气体都在左气缸中。

在初态,气体的压强为,体积为;在末态,气体压强为,体积为(x为左活塞的高度)。由玻意耳-马略特定律得:

解得:     即两活塞的高度差为

⑵当温度由T0上升至T时,气体的压强始终为,设x/是温度达到T时左活塞的高度,由盖·吕萨克定律得: 

活塞对气体做的功为:

在此过程中气体吸收热量

问答题 简答题
单项选择题

People don’t want to buy information online. Why Because they don’t have to. No more than that because they’re used to not paying for it. That’s the conventional wisdom. Slate, Microsoft’s online politics-and-culture magazine, is an oft-cited example of the failed attempts to charge a fee for access to content. So far, for most publishers, it hasn’t worked.

But nothing on the Web is a done deal. In September graphics-soft-ware powerhouse Adobe announced new applications that integrate commerce into downloading books and articles online, with Simon & Schuster, Barnes and Noble, and Salon. corn among its high-profile partners. Some analysts put the market for digitized publishing at more than $100 billion. Of course, if the Internet can generate that kind of money—some might say almost any kind of money—people want in. And this couldn’t come at a better time. Newspaper and magazine writers in particular are increasingly frustrated by their publishers, which post their writings online but frequently don’t pay them extra.

So here’s the good news: Fathrain. com, the third biggest book-seller on the Net—after Amazon. com and Barnesandnoble. corn—is now doing just what the publishing industry that made it a success fears., it’s offering a secure way to pay for downloadable manuscripts online. Fatbrain calls it offshoot eMatter. With it, the company’s executives have the radical notion of ousting publishers from the book-selling business altogether by giving writers 50% of each and every sale (To reel in authors, eMatter is running a 100% royalty promotion until the end of the year. ) Suggested prices to consumers range from a minimum $ 2 to $ 20, depending on the size of the book to download.

"This will change publishing forever!" Chris MaeAskill, co-founder and chief executive of Fatbrain, declares with the bravado of an interior decorator. "With eBay, anybody could sell antiques. Now anybody can be published. "

There’s been no shortage of authors wanting in. Within a few weeks, according to the company, some 2,000 writers signed on to publish their works. Some of this is technical stuff—Fatbrain got where it is by specializing in technical books—but there are some well-known writers like Catherine Lanigan, author of Romancing the Stone, who has put her out-of-print books and a new novella on the site. Another popular draw is Richard Bach, who agreed to post a 23-page short story to the site.

Not everyone thinks downloadable documents are the biggest thing in publishing since Oprah’s Book Club. "I think it will appeal to sellers more than buyers," says Michael May, a digitalcommerce analyst at Jupiter Communications, which released a report that cast doubt on the market’s potential. "A lot of people are going to publish gibberish. The challenge is to ensure the quality of the work. "

Blaine Mathieu, an analyst at Gartner Group’s Dataquest, says, "Most people who want digital content want it immediately, I don’t know if this model would satisfy their immediate need. Even authors may not find that Web distribution of their works is going to bring them a pot of gold. For one thing, it could undermine sales rather than enhance them. For another, anybody could e-mail downloaded copies of manuscripts around town or around the world over the Net without the writer’s ever seeing a proverbial dime. " Softlock. com, Authentica and Fatbrain are trying to head this problem off by developing encryption padlocks that would allow only one hard drive to receive and print the manuscripts. For now, the problem persists.

According to the passage, which of the following is NOT true()

A. Most books sold by Fathrain are technical ones

B. E-publishing will probably not replace the traditional publishing

C. E-publishing companies have the techniques to prevent documents being spread freely on-line

D. Many authors are quite interested in the new form of publishing