题干

4×100m接力赛是奥运会上最为激烈的比赛项目,有甲乙两运动员在训练交接棒的过程中发现,甲短距离加速后能保持9m/s的速度跑完全程.为了确定乙起跑的时机,需在接力区前适当的位置设置标记,在某次练习中,甲在接力区前s0处作了标记,当甲跑到此标记时向乙发出起跑口令,乙在接力区的前端听到口令时立即起跑(忽略声音传播的时间及人的反应时间),已知接力区的长度为L=20m,设乙起跑后的运动是匀加速运动,试求:

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    I'm a 20-year-old boy,and the following is my story.

    A month after I graduated from high school in August,2007,I was coming home from swim practice in the training centre of the city and was involved in a car accident.I was so seriously injured that I was in a coma for more than two months at Prince Georges Hospital.

    I suffered a lot from the experience of dying eight times during my coma and I couldn't open my mouth to talk or to communicate when I eventually came around.At that time,it seemed that walking was never going to happen again due to all the extreme injuries.Just like my body,my dreams were completely destroyed.But I was not going to let my injuries stop me from realizing my dreams.

    After receiving a total of 15 operations and 36 blood transfusions,I had to make every great effort to learn to talk,eat,walk,shower,and live on my own again.When I was out of hospital,I still had to Go to outpatient therapy in Waldorf,Maryland.After I spent a few months in a wheelchair,I took baby steps to walk on my own.It was a miracle that I was able to walk again,but I still wanted to prove that I could not only walk,but also run.When it came true,I wanted to get back into the pool again.After having a few lung tests,I was able to go in the pool a little bit each week. After a few months of swim training,I began my freshman year at St.Mary's College of Maryland and then became a proud member of the swim team.

    By telling my story,I want to make a positive influence on the world.I am just trying to live every day to the fullest and inspire other people never to give up their dreams no matter how bad a situation is to them.I remember when I was still in my hospital bed,I would have my mom and dad push me round in my wheelchair to the other rooms to see the other patients and chat with them and their family members.I wanted to let them know that everything was going to be okay.Somehow,things would work out for the best.