A:用水平力推着购物车前进,推车的力做了功
B:把水桶从地面上提起来,提水桶的力没有做功
C:书静止在水平桌面上,书受到的支持力做了功
D:挂钩上的书包静止时,书包受到的拉力做了功
人体由于营养缺乏引起的病症是( )
A. sofa B. chair C. table D. phone E. fridge
This is my living room. My ____is near the window. The ____is near the door. The____is under the picture. The ____is on the table. Where is the cat? It's on the____
汽车通过拱桥顶点的速度为10m/s时,车对桥的压力为车重的3/4.如果使汽车行驶至桥顶时对桥恰无压力,则汽车速度大小为( )