Two objects on different concentric circular traks (relative period)

[ninjaboy]

Given two particles A and B realizing circular motion respectively on circles with same center o and of radii RA and RB where RA<RB. There angular velocities wA and wB are constant and initially the two objects form an angle θ.
How long should the object A waits before he crosses object B?

Thanks

 

[tiny-tim]

hi ninjaboy! welcome to pf!

show us what you've tried, and where you're stuck, and then we'll know how to help!

 

[ninjaboy]

Thanks for replying, I've done this;

va=Ra*wa
va=Rb*wb

da=va*ta
db=vb*tb

I need to compute the period for the two objects to meet knowing that wa≠wb and that initially they form angle θ.