Two small rings `O` and `O'` are put on two vertical stationery rods `AB` and `A'B'`, respectively. One end of an inextensible thread is tied at point `A'`. The thread passes through ring `O'` and its other end is tied to ring `O`.
Assuming that ring `O'` moves downwards at a constant velocity `v_(1)`, determine the velocity `v_(2)` of the ring `O`, when `/_AOO'=alpha`.