题目

一物体从斜面顶端由静止开始匀加速下滑,到达斜面底部的速度为2 m/s,则经过斜面中点时的速度是_________m/s,通过前一半位移和后一半位移所用时间之比为_________. 答案：解析：物体做初速度为零的匀加速直线运动,由比例可知:通过前一半位移和后一半位移所用时间之比t1∶t2=1∶(-1),则通过前一半位移和通过全程所用时间之比t1∶t=1∶,根据v=at可得:通过斜面中点的速度为1 m/s. 答案：1   1∶(-1) ―Are you still busy?    ―Yes, I ________ my work, and it won’t take long.   A. just finish                                         B. am just finishing C. have just finished                                     D. am just going to finish