A Falling Particle and A Prism

Consider a movable prism of inclined angle θ and mass M. The prism is initially at rest on a frictionless horizontal surface.
A particle of mass m falls toward the prism, and then hits the prism. After the collision, the prism will move and the particle's speed forms an angle φ with the normal of prism's surface, like shown below.
Assume that there's no energy lost during the collision.
a) Find the relation between M, m, θ, and φ!
b) Calculate φ if M=5 kg, m=10 kg, and θ=30 deg!