A:①②③
B:①②④
C:②③④
D:①③④
如图所示,小刚在5s内将一重为540N的物体匀速向上提起1m,拉力为300N.(不计摩擦及绳重)求:⑴小刚拉绳的功率;⑵滑轮组的机械效率.
— What is this English?
— It's a quilt.