题目

       Bernie was smart and wanted to be his own boss. When Bernie was 25, he took a wife. Bernie had saved some money and decided on a dry goods and grocery store combined.        Marie was skilled at arranging the purchase to appeal to customers and Bernie didn’t mind the long hours. He was happy, and life was good. The business thrived until the great depression hit the entire country. No one had money to purchase pretty things or even food. In 1930, Marie had a heart attack and left Bernie alone.        Following Marie’s death, which Bernie felt was brought 某物理兴趣小组研究“力对运动的影响”及“影响摩擦力的因素”．如图，三个滑道的斜面部分完全相同，水平部分材质不同（毛巾、棉衣、木板）．三个相同的小木块分别从三个滑道的同一高度O处从静止释放，在水平面滑行至停止的距离sBC＜sBD＜sBF．（1）控制其他因素均相同，只体现“滑道材质”与“滑行距离”的关系，这种研究方法属于______法．（2）三种滑行的初始段OB均相同，从能量转化的角度分析，从静止释放时，三木块的______能相同，滑到水平部分左端B处时______能相同，则它们的速度______．（3）在该实验时，三木块在水平面部分所受摩擦力的大小关系fBC______fBD______fBF（填不等号），这个实验只能说明物体所受摩擦力与______有关．（4）结合上述实验，推测和猜想：如果滑道水平部分绝对光滑，小木块将做______．