GEEN 1300
Introduction to
Engineering Computing
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Class Meeting 1
Fall 2009
introductions: instructor & assistants
course CULearn site, course information
Homework Assignment #1, due Wed next week
Register your iClicker
http://www.colorado.edu/its/cuclickers/students/register.html
 reminders
 bring USB "thumb" drive & Excel text to lab
 bring iClicker to class from now on
 example application of Excel
1
An Example Problem
Problem statement
A 100 kg sign is hung from the end of a horizontal
support beam that is hinged to a wall. The beam
and sign are supported by a cable that is attached
to the beam and above to the wall. The beam is
2.5 m long and the cable is 3 m long. The beam
and cable weigh a small amount when compared
to
o the
e ssign.
g Find
d the
ea
attachment
ac e pos
position
o o
of the
e
cable to the beam that minimizes the tension in
the cable.
2
1
Diagram with variables shown
c
T
x
M
L
3
Analysis
Static system
Rotational about hinge
Torques must be balanced
cable sign
Ty  TM
Torque balance
Torque = Force * Lever-arm
Torque balance
TM  MgL
Need component of cable
tension in vertical (y) direction
Ty  T cos   x

T
 Ty
c2  x2
cos  
c
T
c2  x2
x  MgL
c
Solve for tension, T
T
MgLc
x c2  x2
4
2
Excel-based Case Study
5
3