题目

If you have no special plans for your holiday, why not spend your time helping others? Don’t listen to people who say that young people today often think only of themselves．It's not true at all．More and more young people in the USA volunteer to Spend their school holidays working for others．And they don't do it for money．Here are some of their stories． Mice Hamilton, 17 I'm going to help the Forest Center build new hiking paths in the mountains．It's going to be terrific. I'll spend the whole summer living in a tent and breathing the clean mountain air. I'm going to sleep under t小兰在探究斜面的机械效率时，在光滑程度一样而倾斜程度不同的斜面上匀速直线拉动物块，（如图所示）并设计表格记录实验数据如下：实验次数斜面的倾斜程度物体重G/N物体上升高度h/m沿斜面拉力F/N物体移动距离 S/m有用功W有/J总功W总/J机械效率η机械效率平均值1较缓5.00.101.60.500.500.8063%2较陡5.00.152.20.500.751.1068%3最陡5.00.250.501.25（1）如图所示第三次实验弹簧测力计的示数为________N，机械效率约为________（精确到百分位）．（2）小兰在对实验数据处理的过程中出现的错误之处是：________．（3）改正错误后，对实验数据进行分析，你对斜面机械效率问题可获得的初步结论是________．