(2) M=J dt 。ml'o 9 dt mg odo 3g cos0de 21 cos0d0 21 0= 1 2 3sn啡- 2 21c O (2) A B t JM d d ω = t ml l mg d d 9 1 cos 6 2 ω θ = dcos θθωω 2 3 d l g = ωω θθ ω dcos 2 3 d 2 π 0 ∫∫ 0 = l g l g l g 2 3 sin 2 3 2 1 2 π 0 2 ω = θ = l 3 g ω = α = 0 θ gm r θ ω ω d d 9 1 2 = ml