There are two popular ways to speed up N-body simulations of planet formation: (i) confine motion to 2 spatial
dimensions (2D), or (ii) to artificially enhance the physical radii of the bodies (this factor is denoted by
A_ref). These short cuts have the same effect of increasing the collision probability between objects. Here, we
have computed the basic collisional parameters for 50 simulations each containing 10 000 fully interacting bodies which
were confined to 2D. Our goals were to find out the probability distribution functions (pdf) of the basic collisional parameters
such as the impact parameter, impact velocity and specific impact energy. Using a simple method we have improved the
determination of the impact parameter whose distribution is uniform; there is no preferred direction (our results does not
support the most likely 45 deg impact angle stated by Shoemaker (1962)).
We show that in most cases the impact velocity is greater
than the mutual escape velocity. The pdf of the impact velocity can be remarkably well fitted by an exponential function. We
present a scaling law of the impact velocity on the A_ref. Using our scaling law future simulations can
accurately compute the real impact velocity when A_ref > 1 and making use of more sophisticated collision
scenarios like the one of Leinhardt & Stewart (2012).
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