题目

如图甲所示，竖直平面内的光滑轨道由倾斜直轨道AB和圆轨道BCD组成，AB和BCD相切于B点，CD连线是圆轨道竖直方向的直径（C，D为圆轨道的最低点和最高点），且∠BOC=θ=37°，圆轨道直径d为0.4m．可视为质点，质量m=0.1kg的小滑块从轨道AB上高H处的某点由静止滑下，（已知sin37°=0.6，cos37°=0.8，g=10m/s2）求： （1）刚好能通过圆轨道最高点D的高度H； （2）若用压力传感器测出滑块经过圆轨道最高点D时对轨道的压力为F，求出压力F与高度H的关系式，并在图乙阅读下面短文，在空白处按要求填入适当的单词或括号内单词的正确形式。Layla and her family were driving to the town park. It was a hot day. She wanted to swim in the lake. As they got out of the car, Layla saw (she) friends."Let's go into the water!" she called. All the kids jumped in (happy).Layla always has fun at the park. In spring, Layla's dad often takes her fishing in (冠词) lake. They usually go early in the morning. The lake water is still (平静的). It is different (介词) the river, which has water that runs byIn summer, (family) have picnics near the lake. The kids play and swim in the lake.In the morning of autumn, the lake has fog (雾) over it. Layla's dad onc (tell) her something about fog: Hot summer days warm the water, and then cool autumn air (move) over the lake's warm water. The water vapor(水蒸汽) in the air gets cool. It (become) small drops of water (水珠). We can see those drops of water hang in the air as fog.Layla loves winter at the park too. The cold (temperature) turn the water into ice. Many people go skating on the ice.The lake looks different at different times of the year, (连词) it is always a good place to have fun!