如图所示，一质量为m、带有电荷量－q的小物体，可以在水平轨道Ox上运动，O端有一与轨道垂直的固定墙．轨道处于匀强电场中，场强大小为E，方向沿Ox轴正方向，小物体以速度v₀从x₀点沿Ox轨道运动，运动时受到大小不变的摩擦力F_f作用，且 F_f<qE．设小物体与墙图碰撞时不损失机械能，且电荷量保持不变，求它在停止运动前所通过的总路程．

    It's going to be Sport Day on Friday. There are some students on the playground.

    They are doing sports. Amy is running. She can run fast. Sam is jumping. He can jump really high. Daming is playing football. He can play it very well. What is Lingling doing? She is playing basketball. She can catch the ball. But she can't catch it very well.