Re: Problem

["Richard W. Tarara" <rtarara@SAINTMARYS.EDU>]

Assuming both charges were originally at rest (somehow), that they are both
free to move,  and that by 'radius' you actually mean just the distance
between the charges, then you can use conservation of momentum to determine
the velocity of the second charge and then use conservation of energy (KE +
PE(e) constant) to solve the rest.

Once you 'see' that by the nature of the problem that the force and
therefore the acceleration is changing with time you should recognize that
simple dynamics/kinematics approaches can't solve the problem, although the
use of differential equations/integrals can.  However, at that point you
should always take a look at whether or not energy/momentum conservation can
be applied, especially when you really are interested in only the initial
and final states of the system.

Rick

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Richard W. Tarara
Associate Professor of Physics
Department of Chemistry & Physics
Saint Mary's College
Notre Dame, IN 46556
219-284-4664
rtarara@saintmarys.edu

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----- Original Message -----
From: "Harry L. Hightower" <htower@BROOKSTONE.GA.NET>
To: <PHYS-L@lists.nau.edu>
Sent: Thursday, January 20, 2000 1:03 AM
Subject: Problem


>         Given the mass of one object as 3.00 X 10^ -3 kg and
> the mass of a second object as 6.00 X 10 ^ -3 kg (both
> objects have the same charge of 8.00 X 10^ -6 C) when
> released the radius between the two becomes 0.100 m
> and the object with a mass of 3.00 X 10^ -3 kg reaches a
> velocity of 125 m/s. How do you find the original radius?