Find all the points along the line passing through both charges

[btpolk]

Homework Statement

For each of the following arrangements of two point charges, find all the points along the line passing through both charges for which the electric potential V is zero (take V = 0 infinitely far from the charges) and for which the electric field E is zero. (Use the following as necessary: Q, d. Enter 0 or ∞ if necessary.)

(a) charges +Q and +2Q separated by a distance d
V = 0: x =
E = 0: x =

(b) charges −Q and +2Q separated by a distance d
V = 0: x =
y =
E = 0: y =

Homework Equations

The Attempt at a Solution

(a) V=0: X=∞

 

[Spinnor]

You got the first part of a right (well they said points, so -∞ is also an solution), take a stab at the second part of a.

For b you will need the relevant equations.

 

[btpolk]

You got the first part of a right (well they said points, so -∞ is also an solution), take a stab at the second part of a.

For b you will need the relevant equations.

For the second part I tried Q+1/4d but it was wrong. I thought that at that point the positive charges would even out at a net electric field of 0.

 

[btpolk]

What relevant equations should I refer to here?

 

[Spinnor]

Electric potential energy,

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elepe.html

Kinetic energy, mV^2/2