题目

质量为2kg的物体被水平力F压在竖直墙上，当水平力F=80N时，物体处于静止.（g取10N/ kg）求：（1）此时物体受到的摩擦力为多大？（2）当水平力减小到40N时，物体恰好沿墙匀速下滑，求物体与墙面之间的动摩擦因数. 答案：1. 20N     2.   0.5    【试题分析】（1）物体受的摩擦力等于物体的重力F=G=mg=20N（2）匀速下滑时滑动摩擦力等于重力μ=F/FN=G/FN=20N÷40N=0.5. ________ the distance was too long and the time was short, we decided not to drive to Florida． [　　] A．Discovering B．To discover C．To have discovered D．Discovered