如图所示，一带电的小球从P点自由下落，P点距场区边界MN高为h，边界MN下方有方向竖直向下、电场场强为E的匀强电场，同时还有匀强磁场，小球从边界上的a点进入电场与磁场的复合场后，恰能作匀速圆周运动，并从边界上的b点穿出，已知ab=L，求：
（1）该匀强磁场的磁感强度B的大小和方向；
（2）小球从P经a至b时，共需时间为多少？
（1）
，方向水平向外
（2）
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| Twelve years ago, my mother gave birth to the beautiful little girl. 1 , we were later given the 2 that this little girl, who was three and a half month old, would only have 14 days on earth. It's hard to understand what kind of 3 you have when you find out that you're 4 something that you don't even know. As time went on, the number of days kept growing, which gave us 5 . When the doctors said that we could take her home, that was 6 reality hit. We had no 7 . I'm from a small town with small hospitals, but when you don't have money, you just don't 8 it. My mother tried for days to get money, but nothing 9 each time. A caseworker (社会工作者) was even doing her best. It's 10 that it almost felt as if we had to 11 a baby from the hospital. One day the caseworker walked into her boss's office to 12 again. As she walked out, 13 down yet again, out of no where a man walked up to her. He 14 her a handful of money and said, "Please give this to the lady in 15 , so she can take her daughter home." She looked down at her hand with tears in her eyes. As she looked back up to thank him, he was 16 . They searched all over the hospital and he was nowhere to be 17 . Thanks to the guy that I will 18 know, we could take home that 19 baby girl that was only given 14 days to live, and celebrated her 12th birthday yesterday. I am grateful to this man and feel that his act of 20 should be shared with everyone. | ||||
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