A small charge q=0.5$=0\mathrm{.}5$ nC is placed distance 2.0$2\mathrm{.}0$ cm away from a stationary charge Q=9.5$=9\mathrm{.}5$ nC.$.$ At that spot charge q experiences acceleration of magnitude 100$100$ m/$/$s2.$2.$ What is the mass of the charge q?$?$