Question

You and a friend are trying to reconstruct an elaborate old-fashioned scientific instrument. Two identical, conducting masses are supposed to hang on massless strings 33cm long. When activated, the device charges the two conductors to a charge of +15 nC while a third conductor is held fixed and charged to +25 nC. The two unknown masses are then supposed to be in equilibrium when they are floating at the same height as the third conductor. When in this state, each string is supposed to make an angle of 17 with the vertical. Over time, the masses have been lost. You and your friend must determine the value of those unknown masses so the device can be restored

Answer 1

From f middot b middot d tan theta = Fe/mg m = F_e/g tan theta m = kq_1 q_2/(d sin theta)^2 times g times tan theta d sin theta = 33 sin (17) = 9.64 cm = 9 times 10^3 times 15 times 25 times 10^-18/(0.964)^2 times 9.8 times tan(17) = 0.12 gm Ans