问题 选择题

两球在光滑水平面上沿同一直线同一方向运动,其质量,速度分别为追上发生碰撞后,两球的速度可能是(    )

A.

B.

C.

D.

答案

答案:A

这是一道同向追及碰撞问题,在分析时应注意考虑三个方面的问题:动量是否守恒,机械能是否增大,是否符合实际物理情景.针对这三点,要逐一验证.取两球碰撞前的运动方向为正,则碰撞前,系统总动量p=mAvA+mBvB="10" kg·m/s,逐一验证各个选项,发现碰撞后,四个选项均满足动量守恒.碰前,系统总动能Ek=mAvA2+mBvB2="22" J.碰后系统总动能应不大于碰前总动能,即Ek′≤22 J,把各选项代入计算,知选项C、D不满足,被排除.对于选项A,虽然满足机械能不增加的条件,但仔细分析,发现vA′>vB′,显然不符合实际情况,故本题正确答案为选项B

完形填空

完形填空(共20分)

It’s a question anyone might ask in the future: Should your household robot be cool? Or practical? For Sony Corporation, robots ought to be entertaining. The company’s 41 robot, SDR—4 X, can sing and dance.

But for automaker Honda Motor Co Ltd, such 42 should perform useful tasks for their 43 masters.

“It is in the end a machine, a 44 ,” said Masato Hirose, Honda’s chief engineer.

Sony’s chief researcher Toshi Doi said robots performing such tasks as 45for ill or disabled people would not necessarily need a human 46  .

“The attractiveness of the SDR—4 X is its 47”, he said.

“It has feelings. It has instincts(直觉).” Drawing from its 48of 60,000 words, an SDR—4 X robot 49 last week that it can ask a 50 in a high voice: “Please 51still for a minute while I memorize your face.”

It also 52 off its ability to walk on uneven(不平的)floors, and come to its owner when it’s 53. While Honda’s robot is 54 used mainly for entertainment, it is 55 that one day it will be a useful companion. So its robot have been 56to be 120cm tall – more than twice the height of the SDR—4 X. Hirose said 120cm is the 57a robot that moves around a home should be.

“If you are going to have something that can move with 58 in a human surroundings(环境), then it is better to 59 the robot like a human,” he said.

Hirose said that he hopes the robot will be 60 enough so that he can buy one for himself and let it get him a beer.

41. A. earliest           B. latest            C. coolest                            D. smallest

42. A. matters          B. people          C. machines              D. inventions

43. A. human            B. own               C. creative                 D. all

44. A. tool                  B. robot             C. toy                          D. slave

45. A. looking            B. working        C. leaving                   D. caring

46. A. form                B. character     C. job                           D. ability

47. A. appearance   B. purpose        C. personality           D. material

48. A. storage           B. use                C. making                   creation

49. A. said                  B. announced  C. showed                  D. imaged

50. A. friend              B. partner                  C. servant                  D. guest

51. A. hold                 B. lie                   C. take                        D. make

52. A. left                            B. showed        C. put                          D. dropped

53.A. tired                 B. called            C. controlled             D. made

54.A. also                   B. still                C. again                      D. even

55. A. sure                 B. hoped           C. reported                D. described

56. A. expected        B. raised           C. proved                   D. designed

57 A. cheapest         B. dearest                  C. smallest                D. biggest

58. A. ease                B. care               C. difficulty                D. foot

59. A. buy                   B. use                C. invest                     D. design

60. A. useful              B. smart            C. cheap                     D. small

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