问题
选择题
—If the traffic hadn't been so heavy, I could have been back by 6 o'clock.
—What a pity! Tina ________ here to see you. [ ]
A. is
B. was
C. would be
D. has been
答案
答案：B
搜题请搜索小程序“爱下问搜题”
—If the traffic hadn't been so heavy, I could have been back by 6 o'clock.
—What a pity! Tina ________ here to see you. [ ]
A. is
B. was
C. would be
D. has been
答案：B
且足够长的平行导轨，
，导轨平面与水平面间的夹角
°，NQ间连接一个
的电阻。一匀强磁场垂直于导轨平面，磁感应强度
。将一根质量
、电阻
的金属棒ab，紧靠NQ放置在导轨上，且与导轨接触良好，导轨的电阻不计。现静止释放金属棒，金属棒沿导轨向下运动过程中始终与NQ平行。已知金属棒与导轨间的动摩擦因数
，当金属棒滑行至cd处时已经达到稳定速度。（g取l0m/s2，sin37°=0.6，cos37°=0.8） 问：