解 建立直角 坐标系Oxy (1)Lo=2r×mP=(∑m2r1)xv=mr2Xv =-0.5amw (2)Lc=riX mivi=(2mi rXv=0 (3)vn=0 L=08 C v O 解:建立直角 坐标系Oxy x y (1)LO =  ri  mivi (2) Lc =  r i  mivi (3) vri = 0 Lcr = 0 = ( mi ri )v = m rcv = - 0.5amvk A = ( mir i )v = 0 rc