加速度与半径平方的倒数成正比:(r1/r2)^2=a2/a1=w2^2*r2/(w1^2*r1)=T1^2*r2/(T2^2*r1)
得T1/T2=(r1/r2)^(3/2)
代入得:Ta:Tb=(2/5)^(3/2)