问题
填空题
一质量为
的物体沿倾角为
的光滑斜面由静止下滑，则t秒内支持力的功率 ，t秒末重力的功率为 。
答案
0，
题目分析：支持力和速度方向是垂直的，所以支持力做功为零，下滑过程中，机械能守恒，所以有：物体下滑的加速度为：
，所以ts末物体的速度为
，故重力的瞬时功率为
点评：计算瞬时功率一般使用公式P=Fv，计算平均功率一般使用公式
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一质量为的物体沿倾角为的光滑斜面由静止下滑，则t秒内支持力的功率 ，t秒末重力的功率为 。
0，
题目分析：支持力和速度方向是垂直的，所以支持力做功为零，下滑过程中，机械能守恒，所以有：物体下滑的加速度为：，所以ts末物体的速度为，故重力的瞬时功率为
点评：计算瞬时功率一般使用公式P=Fv，计算平均功率一般使用公式
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| Each morning, I walked past a security guard (保安). He 1 everyone that walked by him. I 2 how he knew so many people by their first names. The first few times I saw him. I didn't say hello back to him 3 he greeted me. I was lost in my own world. On Monday he asked, "How was your 4 ?" I told him about my visit to my sick, elderly mother. He told me how 5 he was for my mother's sickness. As I walked away, I realized I did not even know his 6 . The following day, I asked,"What's your name?" He answered,"Gary." I said, "I'm Deborah." After that, we talked a couple of times a week. We 7 stories about our weekends, our dreams, and our families. Gary got offered a new job and moved 8 . It has been years since I last spoke to him, yet the memory feels like yesterday. I look back at what became a friendship of sharing stories from the heart. When you say 9 to a stranger (陌生人) you become a pebble (鹅卵石) thrown into a lake. With each ripple (涟漪) you create, you spread 10 that continues to give. | ||||
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