用图所示装置测量滑轮组的机械效率，部分实验数据如下表：

                                                                                                                                                                                                                                                                                            

实验次数	钩码重力Ｇ/Ｎ	钩码上升高度h/cm	拉力Ｆ/Ｎ	绳子自由端移动距离s/cm	机械效率η
1	2.0	5	1.0	15	66.7%
2	4.0	5	1.8	15	74.1%
3	4.0	10	1.8	30	74.1%
4	6.0	5	2.5	15