题型:问答题 简答题 Afghans used to hold big weddings, costing thousands of dollars, in a county _____ the average annual income is less than $400. [ ]A. which B. whose C. where D. what 查看答案
题型:问答题 简答题 (10分)如图所示,质量M的斜面体置于水平面上,其上有质量为m的小物块,各接触面均无摩擦。第一次将水平力F1加在m上;第二次将水平力F2加在M上,两次都要求m与M不发生相对滑动。求:F1∶F2=? 查看答案