题目

词汇 My good friend Tom is an 1____________(澳大利亚的) boy, but now he teaches in Hangzhou, the 2________(省会) Of Zhejiang Province. Though he is a 3___________(外国人), he likes Chinese history very much. He has been studying Chinese for over two years. Now he knows much about it. And he also has 4_________(几个) other hobbies. For example, he likes 5__________(收集) stamps. Now he has more than two 6__________(千) stamps. He says he will sell some to 7__________(筹集) money to help the poor students in his school. So you see, he is 8_________(感兴趣的) in helpi 在科学研究中，可以通过施加适当的电场和磁场来实现对带电粒子运动的控制．如图(1)所示的xOy平面处于匀强电场和匀强磁场中，电场强度E和磁感应强度B随时间t作周期性变化的图象如图(2)所示．x轴正方向为E的正方向，垂直纸面向里为B的正方向．在坐标原点O有一粒子P，其质量和电荷量分别为m和＋q．不计重力．在t＝时刻释放P，它恰能沿一定轨道做往复运动． (1)求P在磁场中运动时速度的大小v0； (2)求B0应满足的关系； (3)在t0(0＜t0＜)时刻释放P，求P速度为零时的坐标．