This question would amplify your skills in Kinematics.
Two rings O and O' are put two vertical stationary rods AB and A'B'. An inextensible thread is fixed at point A' and on the ring O and is passed through the ring O'. Assuming O' moves downwards constantly with , determine velocity if └AOO' is α. If the answer can be expressed as a())/cosα. Find a+b+c
Also try : Optics or ClassicalMechanics