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利用气垫导轨验证机械能守恒定律，实验装置如图所示，水平桌面上固定一倾斜的气垫导轨；导轨上A点处有一带长方形遮光片的滑块，其总质量为M，左端由跨过轻质光滑定滑轮的细绳与一质量为m的小球相连；遮光片两条长边与导轨垂直；导轨上B点有一光电门，可以测量遮光片经过光电门时的挡光时间t，用d表示A点到光电门B处的距离，b表示遮光片的宽度，将遮光片通过光电门的平均速度看作滑块通过B点时的瞬时速度，实验时滑块在A处由静止开始运动．

阅读下列材料，按要求完成各题。

    This is Mr. Wilson's room. It's clean and tidy. It looks like（像） a nice picture. The walls are white and the window is big. You can see a photo of his family and a photo of his girlfriend on the wall. His girlfriend is Peggy Carmen. A yellow desk is near the window. You can see some green plants and five colorful flowers on it. A blue clock is on it, too. It is seven now. A baseball is under his bed. His T-shirt and his bag are on the bed. Look! What's that in the drawer(抽屉) of the desk? Oh, it's Mimi, a cat. It's black. It looks like a hat.