．一弹簧振子做简谐运动，O为平衡位置，当它经过O点时开始计时，_爱下问搜题

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问题选择题

．一弹簧振子做简谐运动，O为平衡位置，当它经过O点时开始计时，经过0.4 s，第一次到达点，再经过0.2 s第二次到达点，则弹簧振子的周期为

A．0.67 s　　　

B．1.67 s

C．2.0 s

D．2.4 s

答案

AC

分析：弹簧振子的周期是振子完成一次全振动的时间，分析振子振动的过程，考虑通过M点双向性，确定周期．

解答：解：作出示意图如图，若从O点开始向右振子按下面路线振动，则振子的振动周期为T₁=4×（0.4+）s=2s，

如图，若从O点开始向左振子按下面路线振动，M₁为M点关于平衡位置O的对称位置．

则振子的振动周期为T₂=0.4s+0.2s+s≈0.67s．

故选AC．

单项选择题

运气学说是古代的（）。

A.医学气象学

B.医学哲学

C.气功医学

D.预防医学

E.养生学说

完形填空

When I was in college twenty-five years ago, I spent four summers working in 36 at a luxury hotel in downtown Chicago. 37 , I was a maid.
I did not enter the world of housekeeping enthusiastically. My friends had 38 jobs such as making ice cream, selling goods at the mall, or life guarding at the outdoor pool. I had been hoping to get a job as an office lady for a famous company: 39 pay, air-conditioned office, the gold standard for summer jobs, as most of us dreamed of. When that 40 , the only option left was to take a train ride downtown each morning to work as a maid.
It was tiring work, cleaning up to eighteen rooms a day. My 41 attitude reflected my disdain(鄙视) for cleaning toilets, 42 bed sheets, dusting, eight hours a day for the comfort of total strangers who 43 left a tip. I thought it was beneathme. My maid work was average 44 the day I was assigned to the eighteenth floor.
That was Lorena’s regular floor. The only time another maid set foot on it was on Lorena’s day off. If you left any water 45 on the mirror, or a hair on the bed, Lorena would hunt you down when she 46 , as I found out firsthand. She’d ended her lecture to me with “ 47 some pride in your work.”
She did. And so did Rosalie, Helen, Annette, and all the other experienced maids. Their devotion to doing a good job and their belief that their work was a 48 of their character stuck with me throughout my 49 career after graduation. I learned a lot from them during those four summers.
Not a week would go without one of them 50 some firm but friendly advice: “Where’s your commode brush? You don’t have one? How do you expect to get that bowl clean?”
Their pride in a job well done was reflected in how they treated 51 . They left the building at the end of the day in nice dresses and 52 makeup. They looked like they could have been attending an afternoon tea. And, 53 often, they were smiling and laughing, cheerfully greeting their co-workers a good evening. When you work with happiness and 54 , a job will be well done. I believe there is 55 in any job if you work hard and try your best.

B．housekeeping

C．In other words

D．On the other hand

B．fell through

C．occasionally

D．professional

A．frustration

D．satisfaction