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## Homework Statement

Assume that a ball of charged particles has a uniformly distributed negative charge density except for a narrow radial tunnel through its center, from the surface on one side to the surface on the opposite side. Also assume that we can position a proton anywhere along the tunnel or outside the ball. Let

*F*R be the magnitude of the electrostatic force on the proton when it is located at the ball's surface, at radius

*R*. As a multiple of

*R*, how far from the surface is there a point where the force magnitude is 0.79

*F*R if we move the proton

**(a)**away from the ball and

**(b)**into the tunnel?

## Homework Equations

F=qE=ma

E=σ/2ξo

a=σe/2εm

## The Attempt at a Solution

I dont even know where to sstart