l=0.99383

g=9.80665

s=NDSolve[{θ''[t]+ g/l Sin[θ[t]]+0.0 θ'[t]==0, θ[0]==Pi/128, θ'[0]==0},θ, {t,0,10}]

Plot[Evaluate[θ[t] /. s],{t,0,10}, PlotStyle-> Automatic]

Plot[Evaluate[D[θ[t],t] /. s],{t,0,10}, PlotStyle-> Automatic]

FindRoot[Evaluate[D[θ[t],t] /. s],{t,2}]