A pendulum is composed of a light rod with length $l$ and an end triangular head with mass $M$ which makes an angle $\alpha$ with the ground. The pendulum is released from an initial angle $\theta_0$ and flows freely. At its lowest position there is a small sphere with mass $m$ at rest. The triangle hits the sphere when it is at its lowest position and the collision is elastic. Find the velocity of the sphere after the collision.
I have been trying to solve this problem for a while, and I can find the velocity of the triangle before the collision (simple conservation of energy), but I don't understand how to formulate the collision problem, as the sphere is supposed to have an initial velocity with a certain angle ($\alpha$, I presume), but I cannot understand why. Thank you for any help you may give me.