The bead has a positive charge and so does the proton (+1.6*10⁻¹⁹ C), so they will repulse each other, sending the proton away from the bead, giving it a negative acceleration. For the magnitude, let's use Coulomb's Law: F = Kqq/r², where F is force, K is the electrostatic constant (9*10⁹ N*m²/C²), the q's are the charges and r is the distance between them. Plugging in values (remember that the nano- prefix corresponds to 10⁻⁹ and the centi- prefix is 10⁻²), we get F = (9*10⁹)*(30*10⁻⁹)(1.6*10⁻¹⁹)/(1.5*10⁻²)² = 1.92 *10⁻¹³ N. Ok, now that we have the force between the glass bead and the proton, we can use Newton's 2nd law: F = ma, where m is mass of the proton (1.67*10⁻²⁷ kg) and a is acceleration, to find the acceleration. Solving for a, a = F/m = (1.92 *10⁻¹³ N)/(1.67*10⁻²⁷ kg) = 1.15*10¹⁴ m/s².
