A:4条
B:3条
C:2条
D:1条
Children ____ ____ ____ like to have their own ideas.
如图所示,工人用滑轮组将重480N的物体以0.2m/s的速度匀速提升2m,滑轮组的机械效率是80%,则该工人做的总功为____J,所用的拉力为____N,拉力做功的功率为____W.