如图4-1-9所示,纸质圆桶以角速度ω绕竖直轴O高速转动,一颗子弹沿圆桶截面直径方向穿过圆桶.若子弹在圆桶转动不到半周的过程中在桶上留下两个弹孔a、b,已知Oa和Ob间的夹角为θ<180°,圆桶截面直径为d,则子弹的速度大小为…( ) 图4-1-9A.dθ(2πω) B.dωθC.dω/(2π-θ) D.dω/(π-θ)
Some passengers complain that it usually _________ so long to fill in travel insurance documents.
[ ]
A.
costs
B.
takes
C.
spends
D.
spares