题目

My mother lived in an old farm house in north Oregon，which was located far from any other neighbors.She lived with her elder brother and sisters.Since there were not enough rooms for them，her two sisters __41__ the bigger bedroom downstairs，her brother in a room down the hall and she slept in the top room of the building.  The first __42__ event that happened in that house was when my mother was about 10 years old.She was staying home sick with her brother.He had gone __43__ to the kitchen when my mother heard a voice calling her name from the bottom of the stairs.The voice was为了只用一根弹簧和一把刻度尺测定某滑块与水平桌面间的动摩擦因数μ（设μ为定值），某同学经查阅资料知：一劲度系数为k的轻弹簧由伸长量为x至恢复到原长过程中，弹力所做的功为。于是他设计了下述实验：第一步，如图所示，将弹簧的一端固定在竖直墙上，弹簧处于原长时另一端坐在位置B，使滑块紧靠弹簧将其压缩至位置A，松手后滑块在水平桌面上运动一段距离，到达位置C时停止。第二步，将滑块挂在竖直放置的弹簧下，弹簧伸长后保持静止状态。请回答下列问题：①你认为，该同学需用刻度尺直接测量的物理量是（写出名称并用符号表示）                                                                             。②用测得的物理量表示滑块与水平桌面间的动摩擦因数μ的计算式：μ=