A:went
B:is going
C:goe
D:will be going
在高速公路的拐弯处,通常路面都是外高内低。如图所示,在某路段汽车向左拐弯,司机左侧的路面比右侧的路面低一些。汽车的运动可看作是做半径为R的圆周运动。设内外路面高度差为h,路基的水平宽度为d,路面的宽度为L。已知重力加速度为g。要使车轮与路面之间的横向摩擦力(即垂直于前进方向)等于零,则汽车转弯时的车速应等于( )
My name is Cathy. I'm a fourteen-year-old girl from England. Now I'm 1 in a middle school.I have to say that I was not good 2 my lessons before. So I was always afraid of exams.
Last week I 3 my end-of-year exams. Today I got my report card. 4 , I did very well. My mom and dad said it was the best report. It was 5 main subjects that the report card talked about, and I felt very 6 today. My teachers ticked( 给…打勾 ) “7 to improve”,“Good” or “Very good”. My English teacher said my English was much better. For math and science I also 8 “ Very good” ticks. All my teachers said I was 9 And at the end of the report card my head teacher said, “A very good 10. Well done!” I am so pleased with it,but I hope I can get a better report next year. I'm sure I can.
①静电力和万有引力都不是通过直接接触而引起的
②库仑定律和万有引力定律分别只适用于点电荷之间和质点之间的相互作用
③带电体都有质量,因此他们之间除了静电力外,还存在万有引力
④氢原子中的电子和原子核之间主要是靠静电力发生相互作用.