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问题 选择题

关于功和能，下列说法中正确的是（　　）

A．小球沿不同路径移动相同的竖直高度时重力做功不一定相同

B．重力势能是物体单独具有的

C．通常规定：弹簧处于原长时弹簧的弹性势能为零

D．能量的耗散反映出自然界中能量是不守恒的

答案

A、重力做功的特点是只跟初末位置有关，跟路径和路程无关，故A错误；

B、重力势能是物体与地球所共有的，故B错误；

C、规定，弹簧在处于原长时弹簧的弹性势能为零，故C正确；

D、自然界中能量是守恒的，故D错误．

故选C

阅读理解

阅读理解。请根据短文内容选择最佳答案。

      My name is Bill. I'm from the USA. My Chinese teacher is Wang Mei. She is a good teacher. I have many

friends at school. Jimmy is my best friend. He's from Canada. He's tall and he has black hair. Mary is a short

girl. She likes elephant. Sandra is from England. She has long brown hair. She likes monkeys. Wang Dong is

from China. He has short black hair. He speaks English well.

1. Wang Mei is Bill's _____________.

A. teacher

B. friend

C. mother

2. _____________ is from Canada.

A. Wang Dong

B. Jimmy

C. Sandra

3. _____________ has brown hair and likes monkeys.

A. Mary

B. Sandra

C. Jimmy

4. Wang Dong is good at (擅长于) _____________.

A. English

B. painting

C. Chinese

5. How many friends does Bill have?

A. Three.

B. Four.

C. Five.
查看答案
选择题

如图，两个半径均为R的1/4光滑圆弧对接于O点，有物体从上面圆弧的某点C以上任意位置由静止下滑（C点未标出），都能从O点平抛出去，则

A．∠CO1O＝60°

B．∠CO1O＝45°

C．落地点距O2最远为2R

D．落地点距O2最近为R
查看答案