问题 选择题

关于加速度的说法,正确的是(   )

A.加速度是矢量,加速度的方向与速度方向相同

B.速度的变化量越大,加速度越大

C.速度的变化率增大,加速度不一定增大

D.加速度增大,速度可能减小

答案

答案:D

题目分析:加速度是矢量,当加速度方向和速度方向相同时,物体做加速运动,相反时,做减速运动,即加速度方向和速度方向没有关系,A错误D正确,加速度,所以速度的变化量大,加速度不一定大,还要看其所用的时间,B错误,加速度表示物体的速度变化快慢的物理量,所以速度的变化率变大,即加速度变大,C错误,

故选D

点评:加速度是表示物体速度变化快慢的物理量,物体有加速度,说明物体的速度一定是变化的,速度可能增加,也可能减小.加速度增大,速度不一定增大.物体的速度很大时,加速度可能为零.加速度减小,速度可能增大.

单项选择题
阅读理解

阅读理解。

      Will there ever be another Einstein? This is the undercurrent (潜流) of conversation at Einstein memorial

meetings throughout the year. A new Einstein will appear, scientists say. But it may take a long time. After all,

more than 200 years separated Einstein from Isaac Newton.

      Many physicists say the next Einstein hasn't been born yet, or is a baby now. That's because the search

for a unified theory that would explain all the forces of nature has pushed current mathematics to its limits.

New math must be created after the problem can be solved.

      But researchers say there are many other factors working against another Einstein appearing anytime soon.

For one thing, physics is a much different field today. In Einstein's day, there were a few thousand physicists

worldwide, and the theorists who could argue with Einstein probably would fit into a streetcar with seats to

spare. Education is different, too. One key aspect of Einstein's training that-is little noticed is the years of

philosophy he read as a teenager-Kant, Schopenhauer and Spinoza, among others. It taught him how to think

independently about space and time and it wasn't long before he became a philosopher himself.

      And Einstein was a clever musician. The interplay between music and math is well-known. Einstein would

play his violin hard as a way to think through a knotty physics problem.

      Today, universities have produced millions of physicists. There aren't many jobs in science for them, so

they go to Wall Street and Silicon Valley to apply their analytical skills. Those who stay in science don't work

alone and they sometimes do experiment together which takes years. 

      It's hard to imagine a renegade (背叛者) like Einstein standing it. "Maybe there is an Einstein out there

today," said Columbia University physicist Brian Greene, "but it would be a lot harder for him to be heard."

1. According to the second paragraph, the next Einstein will _____.[ ]

A. have to create new math

B. create a unified theory

C. have to be born now

D. push math to its limits

2. The underlined words "knotty" in the fourth paragraph means _____.[ ]

A. easy

B. interesting

C. strange

D. difficult

3. Which of the following will be useful for the next Einstein to be born? [ ]

A. There will be music around.

B. There will be no problems to solve.

C. There will be suitable philosophy to study.

D. There are only a few physicists.

4. The bold words "unified theory" in Paragraph 2 refers to _____. [ ]

A. agreement

B. mathematical rule

C. unique idea

D. physical saying