等截面的空心圆轴，两端受2kN・m的扭转力偶矩的作用。若圆轴的内外径之比为0．9，材料的许用剪应力为50MPa，则根据强度条件，轴的外径应为（）mm。
查看答案
The purpose of the flywheel is to （）
A. provide energy to operate the engine between power impulses
B. neutralize the primary inertia force of the crankshaft
C. reduce the shock of starting loads on the main bearings
D. prevent the engine from operating at critical speed
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