①____umbrella ②____old bike ③____hour ④____elephant
如图,小明用动滑轮在10s内将重400N的物体匀速提高了5m ,若这一过程中动滑轮的机械效率是80%,则下列结论中正确的是( )
如图所示,物体A在斜面上由静止开始匀加速滑行距离x1后,又在水平面上匀减速滑行距离x2后停下,测得x2=2x1,物体经过两平面交接处速率不变,则物体在斜面上的加速度a1与在水平面上的加速度a2的大小关系为( )
⑴Are you a teacher? ____ A.No. I am Bill.
⑵Are you hungry?____ B.This is a cat.
⑶Is it a bag?____ C.No. I am not hungry.
⑷Are you Mike?____ D.Yes, it is.
⑸What is this?____ E.Yes, I am.