题目

）如图所示，水平面内有两根互相平行且足够长的光滑金属轨道，它们间的距离L=0.20 m，在两轨道的左端之间接有一个R=0.10W的电阻.在虚线OOˊ(OOˊ垂直于轨道)右侧有方向竖直向下的匀强磁场，磁感应强度B=0.50 T.一根质量m=0.10 kg的直金属杆ab垂直于轨道放在两根轨道上.某时刻杆ab以v0=2.0 m/s且平行于轨道的初速度进入磁场，同时在杆上施加一个水平拉力，使其以a=2.0 m/s2的加速度做匀减速直线运动.杆ab始终与轨道垂直且它们之间保持良好接触. 杆ab和轨道的 阅读理解 　　Robots have been a part of the manufacturing work force for decades－one in 10 auto-workers, for instance, is now made of metal and electronics．Robots for the house have been slower to come．Household chores(家务杂事)are less predictable and repetitive than those of the assembly line(装配线), making them difficult to explain in the simple language of a machine．Then how can we solve this problem? One answer is to design robots that are flexible for specific tasks, such as cacuuming(用真空吸尘器清扫)．Another is to figure out a way to make robots simple－and cheap－enough that ordinary people can build their own from parts and program them to do whatever they please． 　　With funding from Google, Intel and Microsoft, scientists at Carnegie Mellon University(CMU)in pittsburgh have created a series of build-it-yourself robots which they say are simple and cheap enough for almost anyone to create． 　　It starts with a black box called Qwerk－the robot“brain” that CMU built and sells for $349 on its Website．Using off-the-shelf parts(wheels, screwdrivers, electrical tape)and some simple instructions, anybody can build a 10-centimeter-high robot and program the Qwerk brain．You might make a wheeled robot with a video camera that can keep an eye on your house and sound the alarm in case someone enters． 　　Scientists hope that by bringing simple robot technology to the marketplace, they can open up the industry to the greater public－maybe even make robotics fun．They’ve tested prototypes(原型)in classrooms and workshops, and even tried them out with young kids．While most of the robots serve practical uses, their goal, scientists say, is to get the public to start contributing its own designs, and even make robots a form of self-expression．One student, for example, made a robot that sits on the side of the road and when it sees a car going too fast, puts up a sign that says slow down! (1) Which of the following is NOT true according to the passage? [　　] A． Robots have been used in manufacturing for decades． B． Robots are used to do housework more often than in the assembly line． C． Robots make up 10％of the auto-workers nowadays． D． Robots are made of metal and electronics． (2) Researchers at Carnegie Mellon University in pittsburgh get money for their research from________． [　　] A． some IT companies B． the university C． banks D． the government (3) If you want to make a robot that can keep an eye on your house, which of the following might you NOT need? [　　] A． A black box called Qwerk B． Some wheels C． A real gun D． A video camera (4) Scientists brought simple robot technology to the public in order to________． [　　] A． help people solve household chores B． get people to start their own designs C． give people more chances to know robots D． change manufacturing robots into household ones (5) What would be the best title for the passage? [　　] A． Mobile robots B． Home-made robots C． Factory robots D． Teaching robots