题目

When I caught him ______me, I stopped ______things there and started dealing with another shop. A. cheating; buying                              B. to cheat; buying C. cheating; to buy                           D. to cheat; to buy 答案：A 解析: 略（10分）电阻为R的矩形导线框abcd,边长ab=l, ad=h,质量为m，自某一高度自由落体,通过一匀强磁场，磁场方向垂直纸面向里,磁场区域的宽度为h ，如图，若线框恰好以恒定速度通过磁场，则线框内产生的焦耳热为多少？(不考虑空气阻力)