放在水平地面上的一物块,受到方向不变的水平推力F的作用,F的大小与时间t的关系和物块速度v与时间t的关系如图所示。由此两图线可以求得物块的质量m和物块与地面之间的动摩擦因数μ分别为(g=10m/s2)A.m=0.5kg,μ="0.4 " B.m=1.5kg,μ= C.m=0.5kg,μ="0.2 "
I visited Beijing last week.I was in there five days. A. at B. in C. for
Thank you for your help. What ! A.good a boy B. a boy good C. a good boy
This book is mine. But that is . A. your B. yours C. you
Before have lunch, You should . A. tidy the room B.wash your hands C. jump on the bed
Yesterday ______team won. They got seventy points. A. them B. They C. their