题目

根据句意及首字母提示补全单词。 1．My family is very poor, so I can’t a____the price of 100,000 yuan for a piano. 2．We are d______how often we do different activities. 3．He p______speaking English every day. 4．His grandfather r________when he was 60. 5．Last week’s talent show was great s_______. 答案：1．afford         2．discussing    3．practices     4．retired     5．success质量M＝1kg的物体，在水平拉力F的作用下，沿粗糙水平面运动，经过位移4m时，拉力F停止作用，运动到位移是8m时物体停止，运动过程中－S的图线如图所示。求： （1）物体的初速度多大？ （2）物体和平面间的摩擦系数为多大？       （3） 拉力F的大小？（g取）