问题 选择题

以下说法正确的有:                                             ( )

A.加速度不为零的运动,物体的运动速度方向一定发生变化

B.加速度不为零的运动,物体的运动速度大小一定发生变化

C.加速度不为零的运动,速度的大小和方向至少有一个要发生变化

D.物体运动的加速度不为零,但速度却有可能为零

答案

CD

匀变速直线运动,速度方向不变,A选项错;匀变速圆周运动,加速度不为零,物体运动的速度大小不变,B选项错;加速度不为零,物体的运动状态一定发生变化,或者速度的大小变化,或者速度的方向变化,或者速度的方向和大小都发生变化,C选项对;自由落体运动,开始下落的瞬间,速度为零,加速度不为零,D选项对。

单项选择题
完形填空

完形填空(共20小题,每小题1分,满分20分)

Every year, almost 2 million Americans are injured while they're  21 work every day, 240 are killed on the job. The   22   job is cutting down trees. Being a policeman is safer than many jobs, including driving a truck, collecting garbage and   23  airplanes. One of the safest jobs is being a librarian.

The government inspects(检查) most factories and offices.  24 have to   25   fines(罚款) if their factories or offices are unsafe. In California, employers often go to prison if one of their workers is  26  because a factory didn't  27 safety measures. But President Bush cut down the number of government inspectors(检查员)  28 15 percent.   29 , many people say working is less safe now.

For women workers, the greatest danger so far is murder. Forty--two percent of all  30 who died at work were killed. Many of them work  31 clerks in stores   32 they are alone at night. Experts say they can protect themselves by putting the cash desk in full   33  .

The numbers of deaths and accidents at work don't take into  34 people who become sick from   35   that they are exposed to (暴露)at work. Doctors don't know   36 some chemicals cause illness.There are no government rules for many new chemicals.

Inspectors say employers  37 their backs on safety problems because they don't want to pay the bill for fixing them. They also say some workers don't want to complain about dangers because they may  38  their jobs.

The government should force business to improve safety. There's no   39 for workers dying or  40 in an accident that could have been prevented.

21. A. in           B. at             C. on               D. during

22. A. safest        B. most dangerous   C. easiest            D. most tiring

23. A. flying        B. making         C. doing             D. riding

24. A. Officers      B. Workers         C. Employers        D. Employees

25. A. give         B. offer            C. pay              D. buy

26. A. saved        B. hit             C. shot              D. killed

27. A. use          B.do              C. break            D. take

28. A. to           B. by              C. from            D. at

29. A. As a result    B. As              C. At last            D. Then

30. A. adults        B. youths          C. men              D. women

31. A. for          B. as              C. like               D. to

32. A. which        B. that             C. where            D. why

33. A. view         B. opinion         C. scene              D. scenery

34.A thought       B mind           C thinking            D consideration

35. A. machines     B. chemicals        C. air                D. work

36. A. because      B. when            C. whether            D. even if

37. A. do          B. turn             C. make              D. refuse

38. A. lose         B. miss             C. give up            D. save

39. A. need         B. reason           C. time             D. excuse

40. A. injuring      B. being injured      C. be injuring         D. be injured