# Homework Help: Motion of 4 charges positioned in a square shape

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1. Mar 21, 2017

### Berker

1. The problem statement, all variables and given/known data
Four particles with equal charges q and equal masses m are placed on a plane so that
they form the corners of a square with side length a. The charges are then released from
rest at this configuration (shown as (i) in the figure). After the release, the particles
accelerate outward along the directions of the diagonals. As all charges are equal, they
keep the "square shape" they form, i.e., corners always form a square with side length
continuously increasing with time.

(a) Is this a constant-acceleration motion?
(b) Consider the moment of time when the side length has reached the value 2a (shown
as (f ) in the figure). Let v be the common speed of the charges. Find v.
(c) Consider the time when the charges are infinitely far apart (i.e., side length is 1).
Find the common speed V∞ of the charges.

2. Relevant equations
F=[kq(1)q(2)]/r^2
F=q.E
3. The attempt at a solution
I think I do not need to think algebraically.

2. Mar 21, 2017

### Staff: Mentor

Then how are you planning on answering (b) and (c)? Both would appear to require an algebraic answer.

3. Mar 21, 2017

### TJGilb

Just because you don't have values for "a" and "q" doesn't mean you don't need to think algebraically. You have Coulomb's Law as one of your equations. Think about superposition and pick one particle. How will the other particles affect that particle?