A small charged oil drop has a mass of 4.0*10^(-8) kg and a charge of +2.0*10^(-
ID: 1873580 • Letter: A
Question
A small charged oil drop has a mass of 4.0*10^(-8) kg and a charge of +2.0*10^(-5) Coulombs. It enters a box at point (a) with an initial speed of 1.0*10^(4) m/s traveling in the positive x direction. Assume that the positive x direction points to the right. The other end of the box, labeled as point (b), is at an electric potential 3.5*10^(5) Joules per Coulomb higher than point (a). - What is the speed of the oil drop as it reaches point (b)? If the charge does not reach point (b), say so explicitly and explain how you know. - What is the speed of the oil drop as it exits the box? Please show your work and explain. (This problem did not come with a stated distance between points (a) and (b), otherwise, the answer would be obvious).
Explanation / Answer
Initial kinetic energy of the charged particle, Ki = (1/2)*m*vi^2
= (1/2)*4*10^-8*(1*10^4)^2
= 2 J
Workdone by elctric field, W = F*d*cos(180)
= -F*d
= -q*E*d
= -q*E*d
= -q*delta_V
= -2*10^-5*3.5*10^5
= -7 J
clearly Ki < |W|
so, the particle does not reach point b.