题目

There was a young painter who made money by painting portraits. His dream was to _______famous. One day, a rich man asked him to _______ a portrait for him and promised to pay him 10,000 dollars.After a week, the rich man came to_______ the painting. Although the painting was wonderful, he was not _______ with it. He told the young painter, I will only buy this painting for 3,000 dollars. The young painter was _______.He argued with the rich man, _______ the rich man would keep his promise.The rich man _______ , The man in the painting is me. If I don't buy this painting, _______ else will buy如图所示，两根足够长的光滑平行金属导轨MN、PQ间距为l=0.5 m，其电阻不计，两导轨及其构成的平面均与水平面成30°角，完全相同的两金属棒ab、cd分别垂直导轨放置，每棒两端都与导轨始终有良好接触，已知两棒质量均为m=0.02 kg，电阻均为R=0.1 Ω，整个装置处在垂直于导轨平面向上的匀强磁场中，磁感应强度B=0.2 T，棒ab在平行于导轨向上的力F作用下，沿导轨向上匀速运动，而棒cd恰好能够保持静止。取g=10 m/s2，问： (1)通过棒cd的电流I是多少，方向如何？ (2)棒ab受到的力F多大？ (3)棒cd每产生Q=0.1 J的热量，力F做的功W是多少？