题目

Young trees don’t just grow; they develop a personality and learn more about their environment and how they should best behave in it. They also help each other out whenever there’s trouble.Personality, just as among people, varies among trees. Some are anxious, some bold. On the author’s land, there are three oak trees growing close together. One of the oak trees always starts to shed its leaves two weeks earlier than the others. Since they all experience the same temperature, the same soil and the same length of day, such variables can’t be the explanation. So what’s happening? Well如图所示，质量M=kg的木块A套在水平杆上，并用轻绳将木块A与质量m=kg的小球相连。今用跟水平方向成α=300角的力F=N,拉着球带动木块一起向右匀速运动，运动中M、m相对位置保持不变，取g=10m/s2。求：【小题1】运动过程中轻绳与水平方向夹角θ；【小题2】木块与水平杆间的动摩擦因数μ。