质点是理想化的物理模型,下列有关质点的说法中正确的是( )
A:研究车轮的转动时,车轮可当作质点
B:研究月球绕地球运动时,月球可当作质点
C:研究跳水运动员在空中的翻滚动作,跳水运动员可当作质点
D:乒乓球很小,所以在任何情况下都可当作质点
too, lost, red, first, English, eraser, find, number, must, last
Hi, I'm Jenny Brown. Jenny is my ____ name. Brown is my ____ name. I'm an ____ girl. This morning I ____ my pencil box in the library. I ____ find it. My pencil box is ____. In it, you can see an ____ and a set of keys. If you ____ my pencil box, please call me. My telephone ____ is 765-0652. You can e-mail me, ____. My e-mail address(地址) is jenny 1256@ 126.com. Thanks!
一架飞机水平匀速飞行,从飞机上每隔1秒钟释放一个铁球,先后共释放4个.若不计空气阻力,则四个球( )