题干

在探究“物体重力势能的大小与哪些因素有关”的实验中,让不同质量的铁球从同一高度由静止释放,撞击沙坑,根据比较撞击沙坑后留下的印痕深度进行探究,如图所示,下列说法正确的是(  )

A:实验过程中既用到了转换法,也用到了控制变量法

B:铁球从最上在下落的过程中动能一直在减小

C:这样做的目的是研究物体重力势能的大小与质量的关系

D:这样做的目的是研究物体重力势能的大小与高度的关系

上一题 下一题 0.0难度 选择题 更新时间:2018-11-22 07:02:19

答案(点此获取答案解析)

A,C

同类题1

完型填空

话题

体裁

词数

难度

建议用时

3D技术

说明文

245

★★★

5分钟

      The 30th Olympic Games took place in London from July to August in 2012. Luckily, Chinese 1 fans could watch the exciting games in 3D on TV.

     When you watch 3D movies or TV, you have to wear a(n) 2  pair of glasses. The 3D glasses make the pictures from the screen 3they are there in the room with you.

      3D means having three dimensions(维度): width, height and depth. 3D technology is similar to the way that the human brain and eyes work.   4 the pupils(瞳孔) of a person’s eyes are about 6. 5 cm apart, when we look at something, each eye sees it from a different angle (角度). Our eyes 5 the two pictures to our brain, and the brain puts them together. The small 6 between the picture from the right eye and the picture from the left eye allows us to see depth(立体感).

     When we 7 pictures in two dimensions, each eye gets the same information. That is because the picture has no real depth, and there is only one way of looking at it. A 3D movie or TV needs two film projectors(放映机). One projects a left eye picture and the other projects a right eye picture. The 3D glasses allow us to see  8picture in each eye.

      While one 93D films, he feels that he is actually in the same environment as the things he’s watching. 10 , it also has its disadvantages. People with eye problems may get headaches if they spend too much time watching 3D movies.