複選題26. Consider the problem of elastic collision as shown in Fig.26. The masses of the two pucks are equal. Before colliding, the velocity of puck-1 is v₁b, and puck-2 is at rest initially (v₂b=0). Which answers are correct in the followings? (A)(B)v₂₁sinθ + v₁f/2 = v₁b (C)v₂₁cosθ = v₁f/2 (D)θ = 60° (E)θ = 30°