# [LON-CAPA-users] Duplicated ids found

Itay Furman itayf at nospammail.net
Sun Oct 27 11:45:18 EDT 2013

```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, itayf at 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]
```

More information about the LON-CAPA-users mailing list