Electric Potential and Potential Energy

Question

Point A is at an electric potential of +75V and point B is at an electric potential at -75V. The work done by an external force to move a charge from A to B is 7.5 x 10^-4 J. If the charge starts from rest at A and has kinetic energy of 2.4 x 10^-4 J when it reaches B, what is the charge?

Answer 1

Let the charge be q Coulomb.

At A total energy = q75 J.

At B, total energy = -q75 + 2.4x10^-4

 

PE_A+ Work = PE_B + KE_B

q75 +7.5 x 10^-4= -q75 +2.4x10^-4

150q = -5.1x10^-4

q = -5.1x10^-4/150 =-3.4x10^-6

Charge is -3.4x10^-6J (Ans.)