1. The problem statement, all variables and given/known data When an object such as a plastic comb is charged by rubbing it with a cloth, the net charge is typically a few microcoulombs. If that charge is 3.6*10^-6 C, by what percentage does the mass of a 39g comb change during charging? 2. Relevant equations n/a? 3. The attempt at a solution Ok here it goes... total charge/electron charge=number of electrons 3.6*10^-6 / 1.60*10^-19 =2.47*10^13 Electrons number of electrons* mass of electron at rest= change in mass 2.47*10^13 * 9.11*10^-31=2.05*10^-17g change in mass/mass of comb= %change 2.05*10^-17 / .39 = 5.25*10^-17% It says this is wrong, but I don't know of any other way to work this problem.