题目

把物体竖直地挂在劲度系数为1000N/m的弹簧下端，弹簧伸长2cm。如果把物体放在动摩擦因数为0.30的水平地面上，用同一根弹簧沿水平方向拉物体。当物体产生2m/s2的加速度时，弹簧伸长        cm。 答案：1【解析】把物体竖直地挂在劲度系数为1000N/m的弹簧下端，弹簧伸长2cm。设物体的质量为m，根据胡克定律有：F＝mg＝kx1把物体放在水平地面上时，根据牛顿第二定有：kx2－μmg＝ma联立两式解得：x2＝1×10－2m＝1cm。Almost all cultures celebrate the end of one year and the beginning of another in some way.Different cultures celebrate the beginning of a new year in different ways, and at different times on the calendar.Chinese New Year is an important traditional Chinese holiday celebrated at the turn of the Chinese calendar. It is also traditional for every family to thoroughly clean the house, in order to sweep away any ill-fortune and to make way for good incoming luck. Windows and doors will be decorated with red color paper-cuts and couplets with popular themes of “good fortune”or “happiness”, “wealth”, and “longevity”. Other activities include lighting firecrackers and giving money in red paper envelopes.In Western countries, people usually celebrate New Year at midnight on December 31st or January 1st. People may go to parties, sometimes dressed in form alclothes like tuxedos and evening gowns, and they may drink champagne（香槟）at midnight. During the first minutes of the New Year, people cheer and wish each other happiness for the year ahead. But some cultures prefer to celebrate the New Year by waking up early to watch the sun rise.It is also a common Western custom to make a New Year’s promise, called a resolution. New Year’s resolutions usually include promises to try something new or change a bad habit in the New Year.Many cultures also do special things to get rid of bad luck at the beginning of a new year. For example, in Ecuador, families make a big doll from old clothes. The doll is filled with old newspapers and firecrackers. At midnight, these dolls are burned to show the bad things from the past year are gone and the New Year can start afresh. Other common traditions to keep away bad luck in a New Year include throwing things into rivers or the ocean, or saying special things on the first day of the New Year.Other New Year traditions are followed to bring good luck in the New Year. One widespread Spanish tradition for good luck is to eat grapes on New Year’s Day. The more grapes a person eats, the more good luck the person will have in the new coming year. In France, people eat pancakes for good luck at New Year. In the United States, some people eat black-eyed peas for good luck—but to get good luck for a whole year you have to eat 365 of them!1.The passage is mainly about_____.A．the meaning of “Happy New Year!”B．several different New Year traditionsC．traditional activities for the New YearD．interesting traditions on New Year’s Day2. We can learn from the passage that_____.A．some cultures celebrate New Year in the morningB．4 cultures do special things to celebrate New YearC．people in Ecuador go to parties on December 31stor January 1stD．the Western people celebrate New Year only on New Year’s Day3.To have a happy new year,_____.A．friendssing to each other in special waysB．families make big dolls filled with new clothesC．some people get up early to watch the sunriseD．Europeans eat 365 grapes on New Year’s Day4.When eating black-eyed peas on New Year’s Day, people think_____.A．one pea brings one day of good luckB．black-eyed peas are the best medicineC．the peas are very black and taste badD．the peas are helpful to count numbers