题目

质点A、B均做匀变速直线运动，它们的运动规律分别是：sA=2t﹣5t2和sB=5t﹣3t2（位移sA和sB的单位是m，时间t的单位是s），由这两关系式可知（ ） A．质点A的加速度aA=﹣5m/s2 B．质点B的加速度aB=10 m/s2 C．质点A的加速度aA=﹣10m/s2      D．质点B的初速度vB0=3m/s 答案：解：A、C、根据匀变速直线运动的位移时间公式，结合：sA=2t﹣5t2得，质点的初速度vA0=2m/s，加速度：aA=﹣10m/s2．故A错误，C正确； B、D、根据匀变速直线运动的位移时间公式，结合：sB=5t﹣3t2得，质点的初速度vB0=5m/s，加速度：aB=﹣6m/s2．故B错误，D错误． 故选：C综合填空（5分）Large miss move noisy traffic be house quiet live airMany people are ____1.______ from the countryside to cities for work. Cities are_____2.____ and interesting but they are _3._________. The ____4.______traffic is heavy and the cost of living _5._________ high. Now some of these people ___6._____ country life, In the countryside, there are many ___7.______ with big yards. The ___8.________ is fresh and life is ____9._______ . Many people like___10._______ there.