题目

Dear Editor,      I used to be a doctor in the children’s department of a hospital. Sometimes I treated children who had been poisoned by medicine for older family members. The children didn’t know the medicine was dangerous; they just knew it tasted sweet. Children easily open the bottle that we now use in China.      Some days ago I talked about medicines with an American. He showed me a sort of plastic bottle. The design was quite simple and I’m sure our Chinese factories could produce these bottles. The top of the bottle licks but can be opened by pressing down on it （12分）如图所示，水平传送带以速度v1=2m/s匀速向左运动，小物体P、Q通过定滑轮且不可伸长的轻绳相连，mp=2kg，mQ=1kg，已知某时刻P在传送带右端具有向左的速度v2=4m/s，小物块P与传送带之间的动摩擦因数μ=0.1，P与定滑轮之间的轻绳始终保持水平，不计定滑轮的质量和摩擦。小物块P与传送带之间的最大静摩擦力等于滑动摩擦力，传送带、轻绳足够长，g＝10 m/s2．求：(1)小物块p在传送带上向左运动的最大的距离x(2)小物块p离开传送带的时速度大小v