题干

(2015•哈尔滨)小聪测量了如图所示的滑轮组的机械效率,他先后进行了两次实验,将钩码分别匀速竖直提升h1和h2的高度(h1>h2).对两次实验中一些物理量进行比较,正确的是(其中s为绳子自由端通过的距离,H为动滑轮上升的高度)(  )

A:.s1=s2   

B:H1=H2

C:η12  

D:W有用1=W有用2

上一题 下一题 0.0难度 选择题 更新时间:2015-10-29 08:44:05

答案(点此获取答案解析)

C

同类题5

阅读理解

    Michelin inspectors, the super secret spies of the restaurant industry, are the anonymous (匿名的) keepers of the famous Michelin star rating. They've been writing anonymous reports of restaurants for over 100 years.

    “We say it's a little like the CIA,” said inspector “M” with a laugh. She asked that her identity not be revealed. “My whole life is staying under the radar, staying away from cameras, using fake names, trying to steal in and out of restaurants quietly.”

    Along with their boss, Jean Luc Naret, the director of the Michelin Guide, about 90 inspectors around the world decide which restaurants will win the cooking equivalent (等价物) of an Oscar, the Nobel Prize and Megamillions jackpot (百万彩票) all at once. The Michelin Guide covers 23 countries, and out of the 45,000 rated restaurants, less than 100 have the top rating — only nine American restaurants carry three stars.

    If the name “Michelin” brings the tires on your car to mind, you're not too far off. The Michelin rating began in France in 1900 as a marketing trick. The Michelin brothers thought their customers would bum more rubber if given a list of hotels and restaurants to explore.

    Inspector “M” admitted being an inspector leads to a lonely dining life. “Most of the time we dine alone,” she said. “It gives us the ability to really focus on the food and the atmosphere and capture the entire experience.” To cover their tracks, “M” said sometimes two inspectors will dine together and write two separate papers. It's better than saying “table for one”, right?

    “When you're really, really into food and very crazy about food, everything else that's going on around you isn't so important,” she said.