1. The problem statement, all variables and given/known data (see attachment) 2. Relevant equations 3. The attempt at a solution I am not sure about this but as the string is inextensible, the component of velocity of the rings along the string should be equal. O' moves downwards and O moves upwards (not sure but it looks so). Hence, ##v_1\cos \alpha=v_2\cos \alpha \Rightarrow v_1=v_2 ## but this is apparently wrong.