题目

Mobile phone (手机) has become a problem for middle schools. Some middle schools in Australia have banned (禁止) students from carrying mobile phones during school hours. Mobile phone use among children has become a problem for the school this year. Several children have got mobile phones as Christmas gifts, and more students will want them. Mary Bluett, an official, said mobile phone use is a distraction (分心的事) to students during school hours and it also gives teachers so much trouble in their classrooms. Teachers were also saying that sometimes students might use phone 某同学用如图甲所示的装置测量滑块与水平桌面之间的动摩擦因数，实验过程如下：(1)用游标卡尺测量出固定于滑块上的遮光条的宽度d，如图乙，d=____mm。在桌面上合适位置固定好弹簧和光电门，将光电门与数字计时器（图中未画出）连接。(2)用滑块把弹簧压缩到某一位置，测量出滑块到光电门的距离x。释放滑块，测出滑块上的遮光条通过光电门所用的时间t，则此时滑块的速度v= ___（用题中所给字母表示）。(3)通过在滑块上增减砝码来改变滑块的质量m，仍用滑块将弹簧压缩到(2)中的位置，重复(2)的操作，得出一系列滑块质量m与它通过光电门时的速度V的值。根据这些数值，作出图象如图丙所示。已知当地的重力加速度为g。由图象可知，滑块与水平桌面之间的动摩擦因数μ=____；弹性势能EP=____。