Hi,
This is problem a newbie question. But I didn't find information on
this. Sorry for that.
After publishing a problem I get the following error message:
[start]
ERROR: Duplicated ids found, problem will operate incorrectly.
Duplicated ids seen:
11
This error occurred while processing response 12 in part
[end]
I could find in my code only a single id="11".
Note that the numerical ids in
<import id="11">/res/jce/itayf/pub/lib/const_phys.library</import>
and
<numericalresponse unit="C" format="2E" answer="$q" id="12">
were added by lon-capa after publication.
The code follows below.
Thanks in advance,
Itay
[start code]
<problem>
<comment>
File = elec_coulomb_identical-hanging-charges.problem
Author = Itay Furman, PhD, it...@fastmail.fm
Created = 2013-10-08
Updated = 2013-10-08
Version = 0.01
Source = Expanded from a problem by Michael Friedberg, JCE.
</comment>
<import id="11">/res/jce/itayf/pub/lib/const_phys.library</import>
<script type="loncapa/perl">
# Set-up
$k_coulomb = $Coulomb_Const;
$g = 9.8; # Gravity acceleration [m /
s^2].
$len = &random(10, 50, 5); # String length [cm].
$theta = &random(4,25,1); # Angle between string and
vertical [degrees].
$th_rad = $theta* $Pi / 180; # Same angle [rad].
$mass = &random(5,80,5); # Body mass [g].
# Compute the magnitude of the charge on each body.
$q = 2 * ($len/100) * sin($th_rad) * sqrt(($mass/1000) * $g * tan($th_rad)
/ $k_coulomb);
# Note the following factors are required:
# 1/100 in ($len/100) to convert $len: [cm] -> [m].
# 1/1000 in ($mass/1000) to convert $mass: [g] -> [kg].
# $Pi/180 in ($theta*$Pi/180) to convert sin()'s arg: [deg] -> [Rad].
</script>
<startouttext />
<h2>The Electrostatic Force Between a Pair of Identical Hanging Point
Charges</h2>
<p>
Two point bodies, each having a mass of <num>$mass</num> [g], are connected
to identical massless
isolating strings whose length is <num>$len</num> [cm].
The strings are connected to the same hook on the ceiling.
</p>
<p>
The bodies carry identical charges.
Therefore, due to electrostatic repulsion, each string is inclined with an
angle of
$theta<sup>o</sup> relative to the line that pass through the hook and is
orthogonal to the
ceiling.
</p>
<endouttext />
<part id="q" display="Compute the charge.">
<startouttext />
<strong>Compute: </strong> the electric charge on each body is
<endouttext />
<numericalresponse unit="C" format="2E" answer="$q" id="12">
<responseparam name="tol" type="tolerance" default="2%" description="Numerical
Tolerance" />
<textline readonly="no" />
</numericalresponse>
</part>
<img alt="A pair of identical hanging charged masses."
src="/res/jce/itayf/pub/share/img/131012_pair-hanging-charges.jpg"
encrypturl="no" />
<allow
src="/res/jce/itayf/pub/share/img/131012_pair-hanging-charges.jpg" />
</problem>
[end code]
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