According to the conservation of momentum directly, at the moment of explosion, the work done by gravity can be ignored, so the momentum is conserved before and after the explosion, so according to the meaning of the question, the answer can be obtained by drawing.

Let the mass of abc be m, then the mass before explosion is 3m and the momentum is 3mv0. After the explosion, the velocity of A is 0, so we only consider bc, and the velocity of B forms an angle α with the horizontal plane, and the velocity of bc is equal. Draw an image and get an isosceles triangle, and you can get the solution directly.