质量为m的带电小球带电量为+q,用绝缘细线悬挂在水平向左的匀强电场中,平衡时绝缘细线与竖直方向成30°角,重力加速度为g.求电场强度的大小.
小球受力如图,所以
即:
液压泵产生困油现象的原因是什么?
-Do you know why Michael resigned from the board?
-He held out for higher wages, but was ____ in the end.
A.put down
B.broke down
C.cut down
D.turned down