题目

A lot of tents, drinking water and food __________ to the homeless earthquake survivors in the past several weeks. A. are sent                    B. were sent           C. have been sent   D. had been sent 答案：C如图所示，有一半径为R的半圆形圆柱面MPQ，质量为2m的A球与质量为m的B球，用轻质绳连接后挂在圆柱面边缘．现将A球从边缘M点由静止释放，若不计一切摩擦，求（1）A球沿圆柱面滑到最低点P时的速度大小．（2）A球沿圆柱面滑到最低点P的过程中绳子对A，对B，对AB所组成的系统各做多少功．