Two identical positive point charges

PHYSICS · Multi-part · CBSE · Physics · Electrostatic Potential and Capacitance · Electrostatic Potential and Capacitance

Problem

Two identical positive point charges, each of magnitude

+5.0\,\mu\text{C}

, are fixed in space and separated by

0.40\,\text{m}

. A third point charge of

-1.0\,\mu\text{C}

is placed at the midpoint of the line joining the two fixed charges. The third charge has a mass of

4.0\times10^{-4}\,\text{kg}

and is released from rest. Constant:

k = 8.99\times10^{9}\,\text{N}\cdot\text{m}^2/\text{C}^2

. Neglect gravitational forces unless instructed otherwise. (a) Determine the initial electric potential energy of the three-charge system. (b) Calculate the speed of the moving charge after it has traveled to a point very far from the other two charges. (c) Estimate the magnitude of the change in gravitational potential energy of the moving charge during its motion and justify whether it is reasonable to neglect gravity in part (b). Use

g = 9.8\,\text{m/s}^2

and assume the vertical displacement does not exceed

1\,\text{m}

. (d) If one of the fixed positive charges were instead negative with the same magnitude, explain qualitatively how the answer to part (b) would be affected. No numerical calculation is required.

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