问题 计算题

(18分)如图所示,光滑的绝缘平台水平固定,在平台右下方有相互平行的两条边界MN与PQ,其竖直距离为h=1.7m,两边界间存在匀强电场和磁感应强度为B=0.9T且方向垂直纸面向外的匀强磁场,MN过平台右端并与水平方向呈θ=37°.在平台左端放一个可视为质点的A球,其质量为mA=0.17kg,电量为q=+0.1C,现给A球不同的水平速度,使其飞出平台后恰好能做匀速圆周运动.g取10m/s2

(1)求电场强度的大小和方向;

(2)要使A球在MNPQ区域内的运动时间保持不变,则A球的速度应满足的条件?(A球飞出MNPQ区域后不再返回)

(3)在平台右端再放一个可视为质点且不带电的绝缘B球,A球以vA0=3m/s的速度水平向右运动,与B球碰后两球均能垂直PQ边界飞出,则B球的质量为多少?

答案

(1)A球能做圆周运动,必须有:Eq=mAg…

电场强度方向竖直向上…

(2)A球在MNPQ区域运动时间相等,必须从边界MN飞出,

如图所示,

最大半径满足:R/cosθ+R/=hcosθ…

A球做匀速圆周运动有:

解得:vA=0.4m/s…

依题意,A球速度必须满足:0<vA≤0.4m/s…

(3)AB相碰后,A做匀速圆周运动,半径R=h…

得vA=0.9m/s…

B球做平抛运动,设飞行的水平距离为x,时间为t,有:

x=vB0t…

……1分

vB0=vytanθ=gttanθ…

得vB0=3m/s…

由动量守恒定律得:

mAvA0=mAvA+mBvB0

mB=0.119kg…

单项选择题
完形填空

第二节: 完型填空(共20小题;每小题1.5分,满分30分)

阅读下面短文,撑握其大意,然后从31—50各题所给的四个选项(A、B、C和D)中,选出最佳选项,并在答题卡上将该项涂黑。

I believe listening is powerful Medicine.

Studies have shown it takes a(n) __31__ about 18 seconds to __32__ a patient after he begins talking.

It was Sunday. I had one last patient to see. I __33__ her room in a hurry and stood at the doorway. She was an older woman, sitting at the edge of the bed, __34__ to put socks on her swollen feet. I stepped in, spoke quickly to the nurse, __35__ her chart noting she was in stable __36__. I was almost in the clear.

I stood against the bed looking down at her. She asked if I could help put on her socks. __37__, I started a monologue that went something like this: "How are you feeling? Your sugars and blood pressure were high but they're better today. The nurse __38__ you're anxious to see your __39__ who's visiting you today. It's nice to have family visit from far away. I bet you really __40__ forward to seeing him."

She __41__ me with a serious, authoritative voice. "Sit down, doctor. This is my story, not your story."

I was surprised and __42__. I sat down. I helped her with the socks. She began to tell me that her only son lived around the corner from her, but she had not seen him in five years. She believed that the stress of this __43__ greatly to her health problems. After hearing her story and putting on her socks, I asked if there was anything else I could do for her. She shook her head no and smiled. All she wanted me to do was to __44__.

Each __45__ is different. Some are detailed; others are unclear. Some have a beginning, middle and end. Others wander __46__ a clear conclusion. Some are true; others not. __47__ what really matters to the storyteller is that the story is __48__-— without interruption, assumption or __49__.

Listening to someone's story is key to healing and diagnosis. I often thought of what that woman taught me, and I often __50__ myself of the importance of stopping, sitting down and truly listening.

31. A. physicist            B. physician          C. expert               D. dentist

32. A. understand      B. recognize         C. interrupt           D. know

33. A. entered                 B. passed                     C. left                  D. approached

34. A. continuing      B. learning                  C. pretending               D. struggling

35. A. observed            B. scanned               C. designed           D. evaluated

36. A. level                  B. condition          C. position            D. period

37. A. Therefore           B. Otherwise         C. Instead             D. Moreover

38. A. indicated            B. responded         C. mentioned               D. announced

39. A. son                    B. husband                   C. brother             D. nephew

40. A. look                  B. tolerate                    C. chant         D. clarify

41. A. bothered            B. influenced                      C. stopped            D. puzzled

42. A. disappointed       B. scared                    C. thrilled             D. embarrassed

43. A. attached             B. contributed              C. devoted            D. owed

44. A. sit                        B. wait                        C. listen                D. comfort

45. A. feeling                      B. case                        C. life                  D. story

46. A. without              B. to                           C. for                   D. at

47. A. And                   B. Yet                         C. So                   D. Then

48. A. read                   B. written                    C. repeated           D. heard

49. A. judgment           B. acknowledgement      C. encouragement   D. commitment

50. A. convinced          B. informed                 C. reminded          D. Warned