He will not help us with the project, ____ we have to ask somebody else to _____it. A. in this case; be in charge of B. in that case; be in the charge of C. in which case; take charge of D. in its case; take the charge of 答案:C
如图所示,ab是半径为R的圆的一条直径,该圆处于匀强电场中,场强大小为E,方向平行于圆平面.在圆周平面内,将一带正电q的小球从a点以相同的动能抛出,抛出方向不同时,小球会经过圆周上不同的点,在这些所有的点中,经过c点时小球的动能最大.已知∠cab=30°,若不计重力和空气阻力,则电场的方向为
A.
沿a→b
B.
沿a→c
C.
沿O→c
D.
沿b→c