如图所示为匀强电场的电场强度E随时间t变化的图象．当t=0时，在_爱下问搜题

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问题选择题

如图所示为匀强电场的电场强度E随时间t变化的图象．当t=0时，在电场中由静止释放一个带电粒子，设带电粒子只受电场力作用，则下列说法中正确的是（　　）

A．带电粒子将始终向同一个方向运动

B．2s末带电粒子回到原出发点

C．带电粒子在0-3s内的初、末位置间的电势差为零

D．0-2s内，电场力的总冲量为零，电场力的总功不为零

答案

A、带电粒子在前1秒处于匀加速，在第二秒内先做匀减速后反向加速，所以不是始终向一方向运动，故A错误；

B、带电粒子在前1秒处于匀加速，在第二秒内由于加速度大小是之前的2倍，方向与之前相反，因此用去

2

2

秒先做匀减速接着

1-

2

2

秒反向加速．所以2s末带电粒子不在出发点．故B错误；

C、带电粒子在0-3s内的初、末位置间的电场力做功为零，电势能变化为零，则电势差为零．故C正确；

D、0-2s内，电场力的总冲量等于粒子的运量变化，由于电场强度大小不一，所以2秒末速度不为零，因此总冲量不为零．粒子在2秒内没有回到出发点，所以电场力的总功不为零，故D错误；

故选：C

完形填空

“You will never walk again．You will have to use a wheelchair．” I heard his   36  fall heavily on my ears, numbing my soul．If I had never felt hopeless before, I felt hopeless then．
The car accident has left me unconscious．When   37  , I found both legs in casts（石膏）．While I had other serious injuries, my    38  were my first concern．Working as a special needs teacher and busy and active by nature, I couldn’t imagine being   39  in a wheelchair．
Lying in my bed, I wondered how I   40  give my ten-year-old son hope that mom would 41 ．He’d been cheerful on every visit, but I saw    42  in his eyes． He needed the ray of hope that I would not be in a wheelchair forever．
Just maybe, I thought, I could use this experience to teach him what to do when misfortune 43 ．
It didn’t take me long to become 44 with my limited movements and even with the pace the doctors were willing to go with me．I was determined to learn everything they showed me．
Every night in my private room, as soon as I knew I wouldn’t be   45 or discovered, I would move myself from the bed to the floor, 46  on to the bed rail（床栏杆） for dear life, and slowly putting my weight   47  my feet．After several weeks of such difficult   48 , my strength and confidence continued to    49  ．
It came the time to share my accomplishments with the person most    50   to me．One night, when I heard my son greet the nurses at the station, I    51  myself up．As he opened the door, I took a few small steps．   52  , he could only watch as I turned and started back to bed．All of the pain, the fear, and the struggle   53 as I heard the words I had longed to hear, “Mommy, you can walk!”
I am now able to walk alone, sometimes using a stick．I am able to take public transportation to shop and visit friends．My life has been blessed with many   54 of which I am proud．But none has ever brought me the satisfaction and joy   55  by those four little words of my son．

C．explanations

D．surroundings

C．discouraged

B．interrupted

A．Disappointed

B．Embarrassed

A．expectation

C．achievements

判断题

驾驶机动车在道路上超车时可以不使用转向灯。