题目

光滑水平面上，水平恒力F作用在木块上，长木板和木块间无相对滑动，长木板质量为M，木块质量为m。它们共同加速度为a，木块与长木板间的动摩擦因数为μ，则在运动过程中( )A.木块受到的摩擦力一定是μmgB.木块受到的合力小于FC.长木板受到的摩擦力为μmgD.长木板受到的合力为 答案：【答案】BD【解析】由题中“长木板和木块间无相对滑动”可知，本题考查牛顿第二定律、受力分析和摩擦力，根据整体法和隔离法分别进行分析，可求解本题。AC．长木板和木块间无相对滑动，木块受到的摩擦力为静摩擦力，不一定是μmg，根据牛顿第三定律，长木板所受摩擦力也不一定为μmg，故AC错 For a girl who's interested in fashion, what would be the dream job? Being a model? Probably no — that's for a pencil thin who doesn't eat. One answer is, fashion stylist. As more brands open stores in China to expand their reach, the increase in outdoor advertising might light a stylist spark in a girl's heart. Fashion magazine offices are crowded with interns (实习生), and fashionable brand HR managers get thousands of resumes of people looking for a stylist position. "It looked too high before, but now I find it more approachable," said Xue Rui, 22, a Fudan University Chinese literature graduate who works as an assistant stylist at Hermès in Shanghai. "There is no certain principle in dressing up models, and you can try every way with your own distinct taste to make them pretty and attractive." The attractiveness of this line of work is not only in the fabulous clothes. And it's not like it used to be: an insider's job with little recognition and even less money. Now it's a career with a profile, prospects and pay packet. Girls can find it hard to ignore this tempt and the field is opening up to normal girls, not only style or fashion design majors. "A fashion designer knows how to make a dress pretty, but a stylist knows how to make a person beautiful, from head to toe," explained He Qing, 21, a junior in fashion design at the Beijing Institute of Fashion Technology. "You have to be 'all-round': from hair and make up to clothes, shoes, and accessories(配饰) to the event," said He. "You have to know everything, and handle several things at the same time. It's challenging. That's why I love it." It's not, however, without its downside, no matter how great you may think it is, "It's incredibly hard work," said Chen Qianzhu, a stylist at the Chinese version of Elle magazine. "You need to build good relations with various people — stars, photographers, PR managers, other media, even airlines." You need to take care of clothes in the workplace and pay for even a tiny spot you get on them, Chen said. "The worst thing is that you might work extremely hard for a week on some serious photos, but if the chief's not satisfied, you do them all over again." 1. A fashion stylist has to do the following EXCEPT _______. A. make every effort to dress up models B. make a model attractive, from hair to feet C. pay for a tiny stain happening to the clothes D. not to eat and keep a thin figure like a pencil 2. Xue Rui, He Qing and Chen Qianzhu are mentioned in the passage in order to ______. A. show the strengths and weaknesses of the new type of career B. compare the different changes about the occupation C. make the article interesting and convincing D. support an idea by giving enough evidence 3. The underlined world 'all-round' in Paragraph 6 can be replaced by ______. A. all-star     B. all-out        C. all-powerful      D. all-purpose 4. Where can the passage be found? A. In a newspaper.              B. In a magazine. C. In an advertisement.           D. In an essay written by a graduate.