如图所示，某物体自空间O点以水平初速度v0抛出，落在地面上的A点，其轨迹为一抛物线。现仿此抛物线制作一个光滑滑道并固定在与OA完全重合的位置上，然后将此物体从O点由静止释放，受微小扰动而沿此滑道滑下，在下滑过程中物体未脱离滑道。P为滑道上一点，OP连线与竖直成45°角，则此物体
A．由O运动到P点的时间为
B．物体经过P点时，速度的水平分量为 
C．物体经过P点时，速度的竖直分量为
D．物体经过P点时的速度大小为
答案：B
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| I devote myself to music because of my grandmother. My mom and I lived with my grandparents from the time I was two 1 I was eight. And even then, I was at their house before and after school every day while my mother was 2 . Grandma loved music. It was she that first 3 me to Elvis Presley (猫王) as a very young child, and once I heard his music, I was truly in 4 with it. Most five-year-olds ask for 5 for birthdays, but I wanted Elvis' albums. I would play them non-stop and 6 to the music in my grandma's family room though my movements didn't look good. Grandma played the piano and 7 me to sing"America the Beautiful" and"Somewhere over the Rainbow". I 8 started playing music on the piano, and soon Grandma was paying for me to 9 piano lessons from a lady living in the 10 . I would come home from 11 and walk three houses down for my lesson. I 12 took about nine months of lessons, but it was enough to give me a foundation (基础) and 13 me to continue to teach myself. Last month when I came home to visit Grandma in the hospital, I 14 my guitar with me. She was in a lot of pain, but the music seemed to 15 her soul. She had me sing some songs and when I started to sing "Somewhere over the Rainbow", her weakened voice 16 in with mine for a few lines. That experience was one of the most 17 of my lifetime and one I will certainly cherish forever. I told her of my music career and she was very 18 and said,"That's wonderful!" I 19 to play for her throughout the week I was home. My grandma passed away two days ago. In my opinion, part of her will live on through every 20 I write or sing in my life. | ||||
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