1. The problem statement, all variables and given/known data A smooth ring of mass m can slide on a fixed horizontal rod.A string tied to the ring passes over a fixed pulley and carries a mass M(<m).At an instant the angle between the rod and the string is θ.Show that if the ring slides with a speed v,the block descends with a speed v cosθ.With what acceleration will the ring start to move if the system is released from rest at θ=30*? I have attached the figure in a pdf file so that you may see it 2. Relevant equations 3. The attempt at a solution I take z axis downwards,x axis rightwards. The force equations:T cosθ=m D²x Mg-T=M D²z Now,we are to find the constraint equation. I got this:(using the length conservation) √[x²+c²]+z=L...............c is a const Differentiating twice w.r.t. t we get: Dz=-Dx (cosθ) What is annoying me is the (-)ve sign before the ansswer. Somehow this is not correct.Because,in the next part we require this result: D²z=-D²x cosθ+0(initially Dx=0) This gives an error in the final answer. Can anyone please help?