质量为m的通电细杆ab置于倾角为θ的导轨上,导轨宽度为d,杆ab与导轨间的动摩擦因数为μ.有电流时,ab恰好在导轨上静止,如图所示。下图是它的四个侧视图,图中已标出四种可能的匀强磁场方向,其中杆ab与导轨之间的摩擦力可能为零的是: 答案:AB— What’s
the matter?
— His
bike hit a rock and ________. Fortunately, he is slightly hurt.
A.turned over
B.turned down
C.turned up
D.turned away