The particle A is projected from point P with velocity u along the plane and simultaneously another particle B with velocity v at an angle  ‘α’ with vertical. If the particles collide at point Q on the plane, Then

If particles collide at Q, it means their displacement along the plane in same. So their velocity components along the plane should be same.velocity component of particle B along the inclined plane=velocity of particle A⇒ V cos[(90−α)+θ]=u   ⇒Vsin(θ−α)=u