M = m g L/2M = m g L/2 cosθα = M / J = ( m g L/2 cosθ) / (1/3 m L^3) = 3 g cosθ / (2L) m g L/2 = 1/2 (1/3 m L^2) (v/L)^2 , v = √(3 g L)
