小明在“测滑轮组机械效率”的实验中，用如图甲所示的滑轮组进行实验，实验数据如下表。                                                                                                                                                                                                                                                                                            

实验序号	物重 G/N	物体上升 的高度h/cm	测力计的 示数F/N	测力计移动的距离s/cm	机械效 率η
1	2	5	0.9	15	74.1%
2	2	10	0.9	30	74.1%
3	4	10	1.7	30	78.4%
4	6	10	2.5	30