1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution Applying conservation of angular momentum w.r.t center O MvL/4 = (ML2/12+ML2/16)ω , where ω is the angular speed of (rod+spider) This gives ω = (12v/7L) The torque τ acting on the system when the spider is at distance 'r' and the rod has rotated by an angle θ is given by τ = 2Mgrcosθ (1) τ = (dθ/dt)(dI/dt) (2) where I = (ML2/12+Mr2) dI/dt = 2Mr(dr/dt) = 2Mr(dr/dθ)(dθ/dt) (3) From the above equations I get gcosθdθ = ω2dr . Integrating I get v = (7/6)√(gL) I don't know the answer . Is this the correct way to approach the problem ? I would be grateful if somebody could help me with the problem .