题目

--- Have you received Jack’s plan? --- Yes, but I don’t think his plan is ______. A. worth being considered           B. worthy to be considered C. worthy of considering            D. worth to be considered 答案：B(选修1－1的考生做) (8分)如图所示，一长度为R的轻质细绳与质量为m的小球相连，悬挂于O点。现将小球从水平位置P点自由释放。求：（1）当细绳摆到竖直位置时小球的速度大小；（2）当细绳摆到竖直位置时此时小球所受拉力的大小.