（14分）如图，将质量m=1kg的圆环套在固定的倾斜直杆上，杆的倾角为37°，环的直径略大于杆的截面直径．对环施加一位于竖直平面内斜向上与杆夹角为37°的拉力F=10N，使圆环由静止开始沿杆加速度向上运动，已知环与杆间动摩擦因数μ=0.5．（g取10m/s2）求：
（1）F作用2s时圆环的速度是多大？
（2）2s后撤去力F，求圆环继续沿杆上滑的最大距离是多少？
（1）2m/s；（2）0.2m；
题目分析：（1）以圆环为研究对象进行受力分析可得：
2分
2分
1分
2s时圆环的速度：
1分
故解得：
1分
（2）撤去外力后，由牛顿第二定律及运动学公式可得：
2分
1分
1分
1分
2分
| Some pioneering work that began as an attempt to discover ways to increase production efficiency led to the founding of the human relations movement in industry and to the development of motivational skills and tools for managers. In 1927 researchers were involved in determining the optimum amount of lighting, temperature, and humidity (with lighting being considered the most important) for the assembly of electronic components at Western Electric. The researchers found that lighting had no consistent effect on production. In fact, production sometimes increased when lighting was reduced to the level of ordinary moonlight! The important part of this experiment began when two Harvard researchers, Elton Mayo and Fritz Roethlisberger, were brought in to investigate these unexpected results further. They found that workers were responding not to the level of lighting but to the fact that they were being observed by the experimenters. This phenomenon came to be known as the Hawthorne effect since the experiments were conducted at the Western Electric Hawthorne Plant. This was the first documented and widely published evidence of the psychological effects on doing work, and it led to the first serious effort aimed at examining psychological and social factors in the workplace. Further experiments were continued for five years. Generally, the researchers concluded from their experiments that economic motivation (pay) was not the sole source of productivity and, in some cases, not even the most important source. Through interviews and test results, the researchers focused on the effects of work attitudes, supervision, and the peer group and other social forces, on productivity. Their findings laid the groundwork for modem motivation theory, and the study of human factors on the job, which continues to this day in such common practices as selection and training, establishing favorable work conditions, counseling, and personnel operations. The contributions of this experiment shifted the focus of human motivation from economics to a multifaceted approach including psychological and social forces. |
Which of the following is NOT true about the Hawthorne study
A．It was the first documented evidence of the psychological effects on doing work.
B．The Hawthorne study continued for five years.
C．They found that the workers responded not to the level of lighting but to the fact that other work conditions were not favorable.
D．The study changed the focus from economics to a multifaceted approach.