问题 选择题

下列描述中,正确的是(  )

A.加速度在数值上等于单位时间里速度的变化量

B.当物体的加速度越来越小时,物体运动的速度也一定越来越小

C.物体的速度变化量越大,加速度越大

D.物体的速度越大,加速度也越大

答案

A、根据加速度的定义式a=

△v
△t
得知,加速度在数值上等于单位时间里速度的变化量.故A正确.

B、当物体的加速度越来越小时,物体运动的速度不一定越来越小,也可能越来越大,比如汽车以恒定的功率在平直公路上起动时,加速度越来越小,而速度越来越大.故B错误.

C、物体的速度变化量越大,根据a=

△v
△t
可知,加速度不一定越大,还与速度变化所用的时间有关.故C错误.

D、速度与加速度没有直接的关系,则物体的速度越大,加速度不一定越大.故D错误.

故选A

选择题
单项选择题

I remember my math teacher Mr. Young very well. He stood out because the kids made fun of him. He was missing one of his fingers, and always pointed at students with his middle finger.

I was not very good at English and math. No matter how hard I tried, I just could not figure out why I did not understand what all the other kids found so easy to learn.

One day, I was told that if I got one more E on my report card, I would be taken to the" big prison for kids".

I tried really hard for weeks. I just couldn’t understand how to make different parts of members into whole things.

The day before report cards were to come out, I knew that Mr. Young would give me an E ,just like he always did.

I went to Mr. Young and told him that the orphanage was going to send me to the big prison if I got another E on my report card. He told me there was nothing he could do;it would be unfair to the other kids if he gave me a better grade than I had actually earned.

I smiled at him and said, "Mr. Young, do you know how the kids make fun of you because you’re missing your finger" He looked at me, moved his mouth to one side and said nothing.

"They shouldn’t do that to you because you can’t help having a finger, Mr. Young. Just like I can’t help not being able to learn numbers and stuff like that. "I said.

The next day, when I got my report card, I tucked it into one of my books. While on the school bus, I opened it : Geography, B+ ; Mechanical Drawing, C- ; English, D- ; History, C- ; Gym, B+ ; Art, C ; Math, D-.

That math grade was the most favorite one I ever received. Because I knew that someone in the world finally understood what it was like for me to be missing a finger inside my head.

What grade should the boy hive got in the math test this time()

A. D-.

B. B+.

C. D.

D. E.