Elastic collision. I cannot find the after collision velocities (quantity and direction), when 2 spheres strike an immobile sphere. All three of them have the same shape and volume, and the same mass (say e.g. 1 kg each). The two moving ones move parallel to each other with the same velocity u, and during their movement their center is on the same axis, vertical to the axis of their velocity. So at the first moment of the collision, the centres of the three spheres form an equilateral tringle. A link would be very helpful too.