We performed a set of five dissipationless-collapse N-body simulations, starting from the same phase-space configuration: the initial particle distribution follows the Plummer (1911) spherically symmetric density distribution $$\label{eqplum}
\rho(r)={{3 {{M_*}}{r_*}^2 }\over 4 {\pi (r^2 +{r_*}^2)^{5/2}}},$$ where ${{M_*}}$ is the total mass and ${r_*}$ a characteristic radius. The choice of a Plummer sphere as initial condition is quite artificial, and not necessarily the most realistic to reproduce initial conditions in the cosmological context (e.g., Gunn & Gott 1972). We adopt such a distribution to adhere to other papers dealing with collisionless collapse (e.g., Londrillo et al. 1991; NLC06; see also Section \[secdis\], in which we present the results of a set of simulations starting from different initial conditions). The particles are at rest, so the initial virial ratio $2K/|W|=0$. What is different in each simulation is the adopted gravitational potential, which is Newtonian in simulation N, dMOND in simulation D, and MOND with acceleration ratio $\kappa$ in simulations M$\kappa$ ($\kappa$=1, 2, 4). For each simulation we define the dynamical time ${t_{\rm dyn}}$ as the time at which the virial ratio $2K/|W|$ reaches its maximum value. In particular, we find ${t_{\rm dyn}}\sim2{t_{\rm *d}}$ in simulation D, and ${t_{\rm dyn}}\sim2{t_{\rm *n}}$ in simulations 