问题 多选题

甲、乙两物体由同一位置出发沿同一直线运动,其速度图象由图所示,下列说法正确的是(  )

A.甲做匀速直线运动,乙做匀变速直线运动

B.两物体两次相遇的时刻分别为2s末和6s末

C.乙在前4s内的平均速度大于甲的速度

D.2s后甲、乙两物体的速度方向相反

答案

A、甲做匀速直线运动,乙物体前2s做匀加速直线运动,加速度为正方向,后4s做匀减速直线运动,加速度为负方向,所以乙物体全程不是匀变速直线运动,故A错误.

B、甲、乙两物体由同一位置出发;在速度-时间图象中图象与坐标轴围成面积代表位移,时间轴上方位移为正,时间轴下方位移为负;所以前2s内乙的三角形面积等于甲的正方形面积,即位移相同,此时两车相遇;前6s内甲车的矩形面积等于乙车三角形的面积,此时又相遇,故B正确.

C、前4s内甲的位移小于乙的位移,所以甲的平均速度小于乙的平均速度,故C正确.

D、由于在速度-时间图象中,某一点代表此时刻的瞬时速度,时间轴上方速度是正数,时间轴下方速度是负数;所以前6s内甲乙两物体的速度都为正方向,故D错误.

故选:BC

阅读理解

阅读理解。

     If you boss asks you to work in Moscow this year, he'd better offer you more money to do so-or even

double that depending on where you live now. That's because Moscow has just been found to be the world's

most expensive city for the second year in a row by Mercer Human Resources Consulting.

     Using the cost of living in New York as a base, Mercer determined Moscow is 34.4 percent more expensive

including the cost of housing, transportation, food, clothing, household goods and entertainment (娱乐).

     A two-bedroom flat in Moscow now costs $4,000 a month; a CD $24.83, and an international newspaper

$6.30, according to Mercer. By comparison, a fast food meal with a hamburger (汉堡包) is a steal at $4.80.

     London takes the No.2 place, up from No.5 a year ago, thanks to higher cost of housing and a stronger

British pound relative to the dollar. Mercer estimates (估算) London is 26 percent more expensive than New

York these days. Following London closely are Seoul and Tokyo, both of which are 22 percent more expensive

than New York, while No.5 Hong Kong is 19 percent more costly.

     Among North American cities, New York and Los Angeles are the most expensive and are the only two

listed in the top 50 of the world's most expensive cities. But both have fallen since last year's study-New York

came in 15th, down from 10th place, while Los Angeles fell to 42nd from 29th place a year ago. San Francisco

came in a distant third at No. 54, down 20 places from a year earlier.

     Toronto, meanwhile, is Canada's most expensive city but fell 35 places to take 82nd place worldwide. In

Australia, Sydney is the priciest place to live in and No. 21 worldwide.

1. What do the underlined words "a steal" in Paragraph 3 mean?

A. an act of stealing

B. something delicious

C. something very cheap

D. an act of buying

2. London has become the second most expensive city because of _____.

A. the high cost of clothing

B. the stronger pound against the dollar

C. its expensive transportation

D. the high prices of fast food meals

3. Which city is the third most expensive on the list?

A. Tokyo.

B. Hong Kong.

C. Moscow.

D. Sydney.

4. Which city has dropped most on the list in North America?

A. New York.

B. Los Angeles.

C. San Francisco.

D. Toronto.

问答题 简答题