题目

This is What a Real Sliver Dollar Looks Like If you trust in the yen , the euro , and the dollar --------stop reading Because this is a story about the sliver coin , EVERYDODY wants . You read the headlines. You know that troubled economic times have put global currency on a rollercoaster(过山车) ride. But millions have found a smarter way to build long­term value with high­grade collectable silver. And right now, those people are lining up to secure some of the last 2012 U．S.Mint Silver Eagles, America's Newest Silver Eagle Dollars. Today, you can graduate to the front of that 如图所示，电阻不计的平行金属导轨MN和OP放置在水平面内，MO间接有阻值为R=3Ω的电阻.导轨相距d=lm，其间有竖直向下的匀强磁场，磁感强度B=0.5T.质量为m=0.1kg，电阻为r=lΩ的导体棒CD垂直于导轨放置，并接触良好.用平行于 MN的恒力F=1N向右拉动CD。CD受摩擦阻力f恒为0.5N.求 1.CD运动的最大速度是多少? 2.当CD的速度为最大速度的一半时，CD的加速度是多少?