Question

Two stationary positive point charges, charge 1 of magnitude 3.75 nC and charge 2 of magnitude 1.55 nC , are separated by a distance of 36.0 cm . An electron is released from rest at the point midway between the two charges, and it moves along the line connecting the two charges. What is the speed vfinal of the electron when it is 10.0 cm from charge 1?

Answer 1

Charges are and .

Initially the electron is midway between the charges. Distance from either charge to the electron is .

Finally distances from electron to the charges are and .

Electric potential energy of two charges and when separated by a distance is

In the above case, potential energy of electron initially

potential energy of electron finally

Since there are no non-conservative forces acting on the system, energy can be conserved.

Sum of potential energy and kinetic energy is constant.

Speed of electron in the final position is