问题 选择题

如图所示为一质点做简谐运动的位移x与时间t的关系图象,由图可知,质点在t=3s时(  )

A.速度为正的最大值,加速度为零

B.速度为负的最大值,加速度为零

C.速度为零,加速度为正的最大值

D.速度为零,加速度为负的最大值

答案

由图可知,质点在t=3s时,位移为零,故加速度为零,速度最大;

3s后质点位移首先为正,故3s时速度方向为正;

故选A.

单项选择题 A1/A2型题
阅读理解

阅读理解。

     Each time I see a balloon, my mind flies back to a memory of when I was a six-year-old girl. It was a rainy

Sunday and my father had recently died. I asked my mom if Dad had gone to heaven. "Yes, honey. Of course."

she said.

     "Can we write him a letter?"

     She paused, the longest pause of my short life, and answered, "Yes."

     My heart jumped."How? Does the mailman go there?" I asked.

     "No, but I have an idea." Mom drove to a party store and returned with a red balloon. I asked her what it

was for.

     "Just wait, honey. You'll see." Mom told me to write my letter. Eagerly, I got my favorite pen, and poured

out my six-year-old heart in the form of blue ink. I wrote about my day, what I learned at school, how Mom

was doing, and even about what happened in a story I had read. For a few minutes it was as if Dad were still

alive. I gave the letter to Mom. She read it over, and a smile crossed her face.

     She made a hole in the corner of the letter where she looped (缠绕) the balloon string. We went outside

and she gave me the balloon. It was still raining.

     "Okay, on the count of three, let go. One, two, three."

     The balloon, carrying my letter, darted upward against the rain. We watched until it was swallowed by the

mass of clouds.

     Later I realized, like the balloon, that Dad had never let his sickness get him down. He was strong. No

matter what he suffered, he'd persevere, dart up, and finally transcend (超越) this cold world and his sick

body. He rose into sky and became something beautiful. I watched until the balloon disappeared into the gray

and white and I prayed that his strength was hereditary. I prayed to be a balloon.

1. When the girl asked her mother if they could write to her father, her mother ______.

A. felt it hard to answer    

B. thought her a creative girl

C. believed it easy to do so   

D. found it easy to lie

2. When the girl was told that she could send a letter to her father, she ______.

A. jumped with joy             

B. became excited

C. started writing immediately         

D. was worried that it couldn't be delivered

3. In the eyes of the author, what was the rain like?

A. An incurable disease.          

B. An unforgettable memory.

C. The hard time her father had.           

D. The failures her father experienced.

4. What would be the best title for the passage? 

A. An unforgettable experience    

B. The strong red balloon

C. Fly to paradise                       

D. A great father