行星轮系如图2.1所示,均质轮Ⅱ由杆O1O2带动沿固定轮Ⅰ作纯滚动。两轮的半径分别为R1和r2,轮Ⅱ的质量为M,杆O1O2的角速度为ω,则轮Ⅱ的动能为。( )
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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