题目

Frank W. Woolworth was born in Rodman,New York,in 1852. His family was very poor farmers,and there was never enough to eat. Frank decided he did not want to be a farmer. He took a short business course, and went to work as a salesman in a large city. Woolworth realized he had a natural skill for displaying goods to arouse people's interest, but he soon learned something more important. One day his boss told him to sell some odds and ends(小商品)for as much as he could get.Frank put all these things on one table with a sign which said: FIVE CENTS EACH. People fought and pushed to buy the thi如图所示，水平轨道AB段为粗糙水平面，BC段为一水平传送带，两段相切于B点．一质量为m＝1kg的物块(可视为质点)静止于A点，AB距离为x＝2m。已知物块与AB段和BC段的动摩擦因数均为μ＝0.5，g取10m/s2，sin37°=0.6. (1)若给物块施加一水平拉力F＝11N，使物块从静止开始沿轨道向右运动，到达B点时撤去拉力，物块在传送带静止情况下刚好运动到C点，求传送带的长度；(2)在(1)问中，若将传送带绕B点逆时针旋转37°后固定(AB段和BC段仍平滑连接)，要使物块仍能到达C端，则在AB段对物块施加拉力F′应至少多大；(3)若物块以初速度v0从A点开始向右运动，并仍滑上(2)问中倾斜的传送带，且传送带以4m/s速度向上运动，要使物块仍能到达C点，求物块初速度v0至少多大。