An alpha particle, the nucleus of a helium atom, has a mass of 6.7*10-27 kg and a charge of 3.2*10-19C. It floats at rest above a charged horizontal sheet with uniform charge density on its surface.
A) What will be the magnitude and direction of an electric field that will balance its weight?
B) Using Gauss Law find the charge per unit area on the horizontal sheet.
I would use E=ke * q/r2 in the r direction, but I am stuck not knowing where to plug in at.