题型:问答题 简答题 At the first meeting of the central leading group for overall reform,President Xi Jinping urged Officials all efforts to carry out new policiesA.would makeB.must makeC.makeD.made 查看答案
题型:问答题 简答题 如图所示,一个质量为m=2kg的小球在细绳牵引下在光滑水平的平板上以速率v=1.0m/s做匀速圆周运动,其半径r=30cm.现将牵引的绳子迅速放长20cm,使小球在更大半径的新轨道上做匀速圆周运动.求:(1)实现这一过渡所经历的时间;(2)在新轨道上做匀速圆周运动时,小球旋转的角速度;(3)圆周的半径增大后外界对绳子的拉力为多大? 查看答案