Where is your sister? She _____________ in the study.[ ]
A. is
B. am
C. are
答案:A
句型转换。
1. It's time for supper. (同义句)
_______________________________________________________
2. She is often late for school. (反义句)
3. We are learning to fly a kite. (对划线部分提问)
4. I think you want to go home. (否定句)
5. Lucy, do your homework. (用now改句)
如图,长为L的不可伸长的细线,拴一质量为m的小球,一端固定于O点,让其在水平面内做匀速圆周运动(这种运动通常称为圆锥摆运动),如图所示。当摆线L与竖直方向的夹角是α时,求:
(1)线的拉力F;
(2)小球运动的周期。